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137-614: In the IPCC's Sixth Assessment Report the original pathways are now being considered together with Shared Socioeconomic Pathways . There are three new RCPs, namely RCP1.9, RCP3.4 and RCP7. A short description of the RCPs is as follows: RCP 1.9 is a pathway that limits global warming to below 1.5 °C, the aspirational goal of the Paris Agreement . RCP 2.6 is a very stringent pathway. RCP 3.4 represents an intermediate pathway between

274-491: A 0.1% or 0.3% tolerance with historical accuracy) tend to suggest that RCP 3.4 (3.4 W/m^2, 2.0–2.4 degrees Celsius warming by 2100 according to study) is the most plausible pathway. RCP 4.5 is described by the IPCC as an intermediate scenario. Emissions in RCP 4.5 peak around 2040, then decline. According to resource specialists IPCC emission scenarios are biased towards exaggerated availability of fossil fuels reserves; RCP 4.5

411-419: A 3,949-page report, which was then approved by 195 governments. The Summary for Policymakers (SPM) document was drafted by scientists and agreed to line-by-line by the 195 governments in the IPCC during the five days leading up to 6 August 2021. In the report, there are guidelines for both responses in the near term and in the long-term. According to the report, the main source of the increase in global warming

548-451: A consistent time period, assessments can attribute contributions to sea level rise and provide early indications of change in trajectory. This helps to inform adaptation plans. The different techniques used to measure changes in sea level do not measure exactly the same level. Tide gauges can only measure relative sea level. Satellites can also measure absolute sea level changes. To get precise measurements for sea level, researchers studying

685-583: A contribution of working group II (WGII), was published on 28 February 2022. Entitled Climate Change 2022: Impacts, Adaptation & Vulnerability , the full report is 3675 pages, plus a 37-page summary for policymakers . It contains information on the impacts of climate change on nature and human activity. Topics examined included biodiversity loss , migration , risks to urban and rural activities, human health , food security , water scarcity , and energy. It also assesses ways to address these risks and highlights how climate resilient development can be part of

822-493: A front-page story, dedicated to the report The Guardian described the Working Group 1 report as the "starkest warning yet" of "major inevitable and irreversible climate changes". This message was echoed by many media channels after the release of the report. The Working Group 3 report found that there is no evidence that sustainable development requires fossil fuels. Climate journalist Amy Westervelt reacting to

959-523: A key change from the 2007 to the 2014 IPCC report is that the RCPs ignore the carbon cycle by focusing on concentrations of greenhouse gases, not greenhouse gas inputs. The IPCC studies the carbon cycle separately, predicting higher ocean uptake of carbon corresponding to higher concentration pathways, but land carbon uptake is much more uncertain due to the combined effect of climate change and land use changes . The four RCPs are consistent with certain socio-economic assumptions but are being substituted with

1096-487: A larger role over such timescales. Ice loss from Antarctica is likely to dominate very long-term SLR, especially if the warming exceeds 2 °C (3.6 °F). Continued carbon dioxide emissions from fossil fuel sources could cause additional tens of metres of sea level rise, over the next millennia. Burning of all fossil fuels on Earth is sufficient to melt the entire Antarctic ice sheet, causing about 58 m (190 ft) of sea level rise. Year 2021 IPCC estimates for

1233-535: A larger shift towards sustainability. The report was published during the first week of the 2022 Russian invasion of Ukraine . In the context of the conflict, the Ukrainian delegation connected the Russian aggression to the global dependency on oil , and a Russian official, Oleg Anisimov , apologized for the conflict despite the possible repercussions. The Ukrainian delegation also called for news reporting on

1370-475: A mean sea level rise 35% higher than that of RCP 2.6. Many plant and animal species will be unable to adapt to the effects of RCP 4.5 and higher RCPs. In RCP 6, emissions peak around 2080, then decline. The RCP 6.0 scenario uses a high greenhouse gas emission rate and is a stabilisation scenario where total radiative forcing is stabilised after 2100 by employment of a range of technologies and strategies for reducing greenhouse gas emissions. 6.0 W/m refers to

1507-701: A much longer period. Coverage of tide gauges started mainly in the Northern Hemisphere . Data for the Southern Hemisphere remained scarce up to the 1970s. The longest running sea-level measurements, NAP or Amsterdam Ordnance Datum were established in 1675, in Amsterdam . Record collection is also extensive in Australia . They include measurements by Thomas Lempriere , an amateur meteorologist, beginning in 1837. Lempriere established

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1644-508: A period of thousands of years. The size of the rise in sea level implies a large contribution from the Antarctic and Greenland ice sheets. Levels of atmospheric carbon dioxide of around 400 parts per million (similar to 2000s) had increased temperature by over 2–3 °C (3.6–5.4 °F) around three million years ago. This temperature increase eventually melted one third of Antarctica's ice sheet, causing sea levels to rise 20 meters above

1781-576: A range of 28–61 cm (11–24 in). The "moderate" scenario, where CO 2 emissions take a decade or two to peak and its atmospheric concentration does not plateau until the 2070s is called RCP 4.5. Its likely range of sea level rise is 36–71 cm (14–28 in). The highest scenario in RCP8.5 pathway sea level would rise between 52 and 98 cm ( 20 + 1 ⁄ 2 and 38 + 1 ⁄ 2  in). AR6 had equivalents for both scenarios, but it estimated larger sea level rise under both. In AR6,

1918-481: A range with a lower and upper limit to reflect the unknowns. The scenarios in the 2013–2014 Fifth Assessment Report (AR5) were called Representative Concentration Pathways , or RCPs and the scenarios in the IPCC Sixth Assessment Report (AR6) are known as Shared Socioeconomic Pathways , or SSPs. A large difference between the two was the addition of SSP1-1.9 to AR6, which represents meeting

2055-527: A report citing the above commentary shows that RCP8.5 is the best match to the cumulative emissions from 2005 to 2020. According to AR6 coauthors, the probable temperature rise is in the middle of the scenario spectrum that ranges from 1.5 °C to 5 °C, at about 3 °C at the end of the century. It is likely that 1.5 °C will be reached before 2040. The threats from compound impacts are rated higher than in previous IPCC reports. The famous hockey stick graph has been extended. Extreme weather

2192-665: A sea-level benchmark on a small cliff on the Isle of the Dead near the Port Arthur convict settlement in 1841. Together with satellite data for the period after 1992, this network established that global mean sea level rose 19.5 cm (7.7 in) between 1870 and 2004 at an average rate of about 1.44 mm/yr. (For the 20th century the average is 1.7 mm/yr.) By 2018, data collected by Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) had shown that

2329-470: A sharp reduction in greenhouse gas emissions, this may increase to hundreds of millions in the latter decades of the century. Local factors like tidal range or land subsidence will greatly affect the severity of impacts. For instance, sea level rise in the United States is likely to be two to three times greater than the global average by the end of the century. Yet, of the 20 countries with

2466-407: A temporary overshoot of the 1.5 degree limit will lead to negative effects on humans and ecosystems. According to the report: "Depending on the magnitude and duration of overshoot, some impacts will cause release of additional greenhouse gases (medium confidence) and some will be irreversible, even if global warming is reduced (high confidence)". Climate resilient development will be more difficult if

2603-609: A theme echoed by many newspapers as well as political leaders and activists around the world. In April 2016, at the 43rd session which took place in Nairobi , Kenya, the topics for three Special Reports (SR) and one methodology report on Greenhouse Gases (GHG) inventories in the AR6 assessment cycle were decided. These reports were completed in the interim phase since the finalisation of the Fifth Assessment Report and

2740-522: A theme echoed by many newspapers around the world. The Technical Summary (TS) provides a level of detail between the Summary for Policymakers (SPM) and the full report. In addition, an interactive atlas was made "for a flexible spatial and temporal analysis of both data-driven climate change information and assessment findings in the report". The Working Group 1 (WGI) report, Climate Change 2021: The Physical Science Basis comprises thirteen chapters and

2877-593: A version of SSP5-8.5 where these processes take place, and in that case, sea level rise of up to 1.6 m ( 5 + 1 ⁄ 3  ft) by 2100 could not be ruled out. The greatest uncertainty with sea level rise projections is associated with the so-called marine ice sheet instability (MISI), and, even more so, Marine Ice Cliff Instability (MICI). These processes are mainly associated with West Antarctic Ice Sheet, but may also apply to some of Greenland's glaciers. The former suggests that when glaciers are mostly underwater on retrograde (backwards-sloping) bedrock,

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3014-633: Is a "very stringent" pathway. According to the IPCC, RCP 2.6 requires that carbon dioxide (CO 2 ) emissions start declining by 2020 and go to zero by 2100. It also requires that methane emissions ( CH 4 ) go to approximately half the CH 4 levels of 2020, and that sulphur dioxide (SO2) emissions decline to approximately 10% of those of 1980–1990. Like all the other RCPs, RCP 2.6 requires negative CO 2 emissions (such as CO 2 absorption by trees). For RCP 2.6, those negative emissions would be on average 2 Gigatons of CO 2 per year (GtCO 2 /yr). RCP 2.6

3151-462: Is a new pathway with a rather low radiative forcing of 1.9 W/m in 2100 to model how people could keep warming below the 1.5 °C threshold. But, even in this scenario, the global temperature peaks at 1.6 °C in the years 2041–2060 and declines after. The IPCC Sixth report did not estimate the likelihoods of the scenarios but a 2020 commentary described SSP5–8.5 as highly unlikely, SSP3–7.0 as unlikely, and SSP2–4.5 as likely. However,

3288-402: Is by lowering the global temperature to 1 °C (1.8 °F) below the preindustrial level. This would be 2 °C (3.6 °F) below the temperature of 2020. Other researchers suggested that a climate engineering intervention to stabilize the ice sheet's glaciers may delay its loss by centuries and give more time to adapt. However this is an uncertain proposal, and would end up as one of

3425-454: Is due to the high level of inertia in the carbon cycle and the climate system, owing to factors such as the slow diffusion of heat into the deep ocean , leading to a longer climate response time. A 2018 paper estimated that sea level rise in 2300 would increase by a median of 20 cm (8 in) for every five years CO 2 emissions increase before peaking. It shows a 5% likelihood of a 1 m ( 3 + 1 ⁄ 2  ft) increase due to

3562-560: Is due to the increase in CO 2 emissions, stating that it is likely or very likely to exceed 1.5 °C under higher emission scenarios. According to the WGI report, it is only possible to avoid warming of 1.5 °C (2.7 °F) or 2.0 °C (3.6 °F) if massive and immediate cuts in greenhouse gas emissions are made. The Guardian described the report as "its starkest warning yet" of "major inevitable and irreversible climate changes",

3699-400: Is expected to increase in line with temperature, and compound effects (such as heat and drought together) may impact more on society. The report includes a major change from previous IPCC in the ability of scientists to attribute specific extreme weather events. The global carbon budget to keep below 1.5 °C is estimated at 500 billion more tonnes of greenhouse gas , which would need

3836-427: Is focused on the foundational consensus of the climate science behind the causes and effects of human greenhouse gas emissions. Compared with previous assessments, the report included much more detail on the regional effects of climate change , although more research is needed on climate change in eastern and central North America . Sea-level rise by 2100 is likely to be from half to one metre, but two to five metres

3973-443: Is likely to keep global temperature rise below 2 °C by 2100. RCP 3.4 represents an intermediate pathway between the "very stringent" RCP2.6 and less stringent mitigation efforts associated with RCP4.5. As well as just providing another option a variant of RCP3.4 includes considerable removal of greenhouse gases from the atmosphere . A 2021 paper suggests that the most plausible projections of cumulative CO 2 emissions (having

4110-531: Is nearly seven times the pre-industrial level. For the extended RCP2.6 scenario, global warming of 0.0 to 1.2 °C is projected for the late 23rd century (2281–2300 average), relative to 1986–2005. For the extended RCP8.5, global warming of 3.0 to 12.6 °C is projected over the same time period. IPCC Sixth Assessment Report The Sixth Assessment Report ( AR6 ) of the United Nations (UN) Intergovernmental Panel on Climate Change (IPCC)

4247-439: Is not ruled out, as ice sheet instability processes are still poorly understood. The report quantifies climate sensitivity as between 2.5 °C (4.5 °F) and 4.0 °C (7.2 °F) for each doubling of carbon dioxide in the atmosphere , while the best estimate is 3 °C. In all the represented Shared Socioeconomic Pathways the temperature reaches the 1.5 °C warming limit, at least for some period of time in

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4384-465: Is now unstoppable. However the temperature changes in future, the warming of 2000–2019 had already damaged the ice sheet enough for it to eventually lose ~3.3% of its volume. This is leading to 27 cm ( 10 + 1 ⁄ 2  in) of future sea level rise. At a certain level of global warming, the Greenland ice sheet will almost completely melt. Ice cores show this happened at least once over

4521-418: Is projected for the late 23rd century (2281–2300 average), relative to 1986–2005. For the extended RCP8.5, global warming of 3.0 to 12.6 °C is projected over the same time period. The RCPs are consistent with a wide range of possible changes in future anthropogenic (i.e., human) greenhouse gas emissions , and aim to represent their atmospheric concentrations. Despite characterizing RCPs in terms of inputs,

4658-520: Is the East Antarctic Ice Sheet (EAIS). It is 2.2 km thick on average and holds enough ice to raise global sea levels by 53.3 m (174 ft 10 in) Its great thickness and high elevation make it more stable than the other ice sheets. As of the early 2020s, most studies show that it is still gaining mass. Some analyses have suggested it began to lose mass in the 2000s. However they over-extrapolated some observed losses on to

4795-409: Is the fastest it had been over at least the past 3,000 years. While sea level rise is uniform around the globe, some land masses are moving up or down as a consequence of subsidence (land sinking or settling) or post-glacial rebound (land rising as melting ice reduces weight). Therefore, local relative sea level rise may be higher or lower than the global average. Changing ice masses also affect

4932-462: Is the largest and most influential scientific organization on climate change, and since 1990, it provides several plausible scenarios of 21st century sea level rise in each of its major reports. The differences between scenarios are mainly due to uncertainty about future greenhouse gas emissions. These depend on future economic developments, and also future political action which is hard to predict. Each scenario provides an estimate for sea level rise as

5069-419: Is the most probable baseline scenario (no climate policies) taking into account the exhaustible character of non-renewable fuels. According to the IPCC, RCP 4.5 requires that carbon dioxide (CO 2 ) emissions start declining by approximately 2045 to reach roughly half of the levels of 2050 by 2100. It also requires that methane emissions ( CH 4 ) stop increasing by 2050 and decline somewhat to about 75% of

5206-492: Is the sixth in a series of reports which assess the available scientific information on climate change . Three Working Groups (WGI, II, and III) covered the following topics: The Physical Science Basis (WGI); Impacts, Adaptation and Vulnerability (WGII); Mitigation of Climate Change (WGIII). Of these, the first study was published in 2021, the second report February 2022, and the third in April 2022. The final synthesis report

5343-784: Is unevenly distributed and many initiatives prioritise immediate risks over longer-term transformational changes. Still, there are feasible and effective adaptation options available and many adaption actions have benefits beyond reducing climate risks, including positive effects on the Sustainable Development Goals . For example, the majority of current adaptations address water-related risks; adaptations like improved water management, water storage and irrigation reduce vulnerability and can also provide economic and ecological benefits. Similarly, adaptation actions like agroforestry, farm- and landscape diversification and urban agriculture can increase food availability, while at

5480-444: The CH 4 levels of 2040, and that sulphur dioxide (SO2) emissions decline to approximately 20% of those of 1980–1990. Like all the other RCPs, RCP 4.5 requires negative CO 2 emissions (such as CO 2 absorption by trees). For RCP 4.5, those negative emissions would be 2 Gigatons of CO 2 per year (GtCO 2 /yr). RCP 4.5 is more likely than not to result in global temperature rise between 2 °C and 3 °C, by 2100 with

5617-529: The Amundsen Sea Embayment played a disproportionate role. The median estimated increase in sea level rise from Antarctica by 2100 is ~11 cm (5 in). There is no difference between scenarios, because the increased warming would intensify the water cycle and increase snowfall accumulation over the EAIS at about the same rate as it would increase ice loss from WAIS. However, most of

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5754-502: The Earth 's temperature by many decades, and sea level rise will therefore continue to accelerate between now and 2050 in response to warming that has already happened. What happens after that depends on human greenhouse gas emissions . If there are very deep cuts in emissions, sea level rise would slow between 2050 and 2100. It could then reach by 2100 slightly over 30 cm (1 ft) from now and approximately 60 cm (2 ft) from

5891-599: The Pacific Decadal Oscillation (PDO) and the El Niño–Southern Oscillation (ENSO) change from one state to the other. The PDO is a basin-wide climate pattern consisting of two phases, each commonly lasting 10 to 30 years. The ENSO has a shorter period of 2 to 7 years. The global network of tide gauges is the other important source of sea-level observations. Compared to the satellite record, this record has major spatial gaps but covers

6028-605: The SROCC assessed several studies attempting to estimate 2300 sea level rise caused by ice loss in Antarctica alone, arriving at projected estimates of 0.07–0.37 metres (0.23–1.21 ft) for the low emission RCP2.6 scenario, and 0.60–2.89 metres (2.0–9.5 ft) in the high emission RCP8.5 scenario. This wide range of estimates is mainly due to the uncertainties regarding marine ice sheet and marine ice cliff instabilities. The world's largest potential source of sea level rise

6165-637: The bedrock underlying the WAIS lies well below sea level, and it has to be buttressed by the Thwaites and Pine Island glaciers. If these glaciers were to collapse, the entire ice sheet would as well. Their disappearance would take at least several centuries, but is considered almost inevitable, as their bedrock topography deepens inland and becomes more vulnerable to meltwater, in what is known as marine ice sheet instability. The contribution of these glaciers to global sea levels has already accelerated since

6302-430: The ice shelves propping them up are gone. The collapse then exposes the ice masses following them to the same instability, potentially resulting in a self-sustaining cycle of cliff collapse and rapid ice sheet retreat. This theory had been highly influential - in a 2020 survey of 106 experts, the 2016 paper which suggested 1 m ( 3 + 1 ⁄ 2  ft) or more of sea level rise by 2100 from Antarctica alone,

6439-474: The shared socioeconomic pathways which are anticipated to provide flexible descriptions of possible futures within each RCP. The RCP scenarios superseded the Special Report on Emissions Scenarios projections published in 2000 and were based on similar socio-economic models. RCP 1.9 is a pathway that limits global warming to below 1.5 °C, the aspirational goal of the Paris Agreement . RCP 2.6

6576-407: The very stringent RCP2.6 and less stringent mitigation efforts associated with RCP4.5. RCP 4.5 is described by the IPCC as an intermediate scenario . In RCP 6, emissions peak around 2080, then decline. RCP7 is a baseline outcome rather than a mitigation target. In RCP 8.5 emissions continue to rise throughout the 21st century. For the extended RCP2.6 scenario, global warming of 0.0 to 1.2 °C

6713-973: The 19th century. With high emissions it would instead accelerate further, and could rise by 1.0 m ( 3 + 1 ⁄ 3  ft) or even 1.6 m ( 5 + 1 ⁄ 3  ft) by 2100. In the long run, sea level rise would amount to 2–3 m (7–10 ft) over the next 2000 years if warming stays to its current 1.5 °C (2.7 °F) over the pre-industrial past. It would be 19–22 metres (62–72 ft) if warming peaks at 5 °C (9.0 °F). Rising seas affect every coastal and island population on Earth. This can be through flooding, higher storm surges , king tides , and tsunamis . There are many knock-on effects. They lead to loss of coastal ecosystems like mangroves . Crop yields may reduce because of increasing salt levels in irrigation water. Damage to ports disrupts sea trade. The sea level rise projected by 2050 will expose places currently inhabited by tens of millions of people to annual flooding. Without

6850-584: The Antarctic continent stores around 60% of the world's fresh water. Excluding groundwater this is 90%. Antarctica is experiencing ice loss from coastal glaciers in the West Antarctica and some glaciers of East Antarctica . However it is gaining mass from the increased snow build-up inland, particularly in the East. This leads to contradicting trends. There are different satellite methods for measuring ice mass and change. Combining them helps to reconcile

6987-503: The Earth was 2 °C (3.6 °F) warmer than pre-industrial temperatures was 120,000 years ago. This was when warming due to Milankovitch cycles (changes in the amount of sunlight due to slow changes in the Earth's orbit) caused the Eemian interglacial . Sea levels during that warmer interglacial were at least 5 m (16 ft) higher than now. The Eemian warming was sustained over

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7124-438: The Greenland ice sheet between 1992 and 2018 amounted to 3,902 gigatons (Gt) of ice. This is equivalent to a SLR contribution of 10.8 mm. The contribution for the 2012–2016 period was equivalent to 37% of sea level rise from land ice sources (excluding thermal expansion). This observed rate of ice sheet melting is at the higher end of predictions from past IPCC assessment reports. In 2021, AR6 estimated that by 2100,

7261-495: The IPCC Fifth Assessment Report (IPCC AR5 WG1) are tabulated below. The projections are relative to temperatures and sea levels in the late 20th to early 21st centuries (1986–2005 average). Temperature projections can be converted to a reference period of 1850–1900 or 1980–99 by adding 0.61 or 0.11 °C, respectively. Across all RCPs, global mean temperature is projected to rise by 0.3 to 4.8 °C by

7398-604: The Last Interglacial SLR is unlikely to have been higher than 2.7 m (9 ft), as higher values in other research, such as 5.7 m ( 18 + 1 ⁄ 2  ft), appear inconsistent with the new paleoclimate data from The Bahamas and the known history of the Greenland Ice Sheet. Even if the temperature stabilizes, significant sea-level rise (SLR) will continue for centuries, consistent with paleo records of sea level rise. This

7535-649: The Road", SSP3 "A Rocky Road", SSP4 "A Road Divided", and SSP5 "Taking the Highway", which have been published in 2016. Those pathways assume that international cooperation and worldwide increase in GDP will facilitate adaptation to climate change. The geopolitical pathways served as one of the sources for the formation of the Shared Socioeconomic Pathways in the report among with other sources. One of

7672-605: The SSP1-1.9 scenario would result in sea level rise in the 17–83% range of 37–86 cm ( 14 + 1 ⁄ 2 –34 in). In the SSP1-2.6 pathway the range would be 46–99 cm (18–39 in), for SSP2-4.5 a 66–133 cm (26– 52 + 1 ⁄ 2  in) range by 2100 and for SSP5-8.5 a rise of 98–188 cm ( 38 + 1 ⁄ 2 –74 in). It stated that the "low-confidence, high impact" projected 0.63–1.60 m (2–5 ft) mean sea level rise by 2100, and that by 2150,

7809-473: The SSP1-2.6 pathway results in a range of 32–62 cm ( 12 + 1 ⁄ 2 – 24 + 1 ⁄ 2  in) by 2100. The "moderate" SSP2-4.5 results in a 44–76 cm ( 17 + 1 ⁄ 2 –30 in) range by 2100 and SSP5-8.5 led to 65–101 cm ( 25 + 1 ⁄ 2 –40 in). This general increase of projections in AR6 came after the improvements in ice-sheet modeling and the incorporation of structured expert judgements. These decisions came as

7946-463: The US's National Oceanic and Atmospheric Administration , stated that his agency "will use the new insights from this IPCC report to inform the work it does with communities to prepare for, respond to, and adapt to climate change". The United States special presidential envoy for climate , John Kerry , said about the Working Group 2 report: "We have seen the increase in climate-fuelled extreme events, and

8083-561: The WAIS to contribute up to 41 cm (16 in) by 2100 under the low-emission scenario and up to 57 cm (22 in) under the highest-emission one. Ice cliff instability would cause a contribution of 1 m ( 3 + 1 ⁄ 2  ft) or more if it were applicable. The melting of all the ice in West Antarctica would increase the total sea level rise to 4.3 m (14 ft 1 in). However, mountain ice caps not in contact with water are less vulnerable than

8220-444: The amount of sea level rise over the next 2,000 years project that: Sea levels would continue to rise for several thousand years after the ceasing of emissions, due to the slow nature of climate response to heat. The same estimates on a timescale of 10,000 years project that: Variations in the amount of water in the oceans, changes in its volume, or varying land elevation compared to the sea surface can drive sea level changes. Over

8357-420: The assumptions is that enough GDP and technology derived from fossil fuels development will permit to adapt even to 5.0 °C (9.0 °F) temperature rise. Some experts assume, that while the odds for a worst-case scenario (5 °C) and the best base-case (1.5 °C) today seem lower, the most plausible outcome is around 3.0 °C (5.4 °F). Sequence of release dates of special IPCC reports during

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8494-574: The average sea level rose by 15–25 cm (6–10 in), with an increase of 2.3 mm (0.091 in) per year since the 1970s. This was faster than the sea level had ever risen over at least the past 3,000 years. The rate accelerated to 4.62 mm (0.182 in)/yr for the decade 2013–2022. Climate change due to human activities is the main cause. Between 1993 and 2018, melting ice sheets and glaciers accounted for 44% of sea level rise , with another 42% resulting from thermal expansion of water . Sea level rise lags behind changes in

8631-422: The average world ocean temperature by 0.01 °C (0.018 °F) would increase atmospheric temperature by approximately 10 °C (18 °F). So a small change in the mean temperature of the ocean represents a very large change in the total heat content of the climate system. Winds and currents move heat into deeper parts of the ocean. Some of it reaches depths of more than 2,000 m (6,600 ft). When

8768-719: The basis for worst-case climate change scenarios. Since the publication of the IPCC Fifth Assessment Report (2014) the likelihood of this RCP has been debated, due to overestimation of projected coal outputs. On the other hand, many uncertainties remain on carbon cycle feedbacks, which could lead to warmer temperatures than projected in representative concentration pathways. RCP 8.5 is still used for predicting mid-century (and earlier) emissions based on current and stated policies. Mid- and late 21st-century (2046–2065 and 2081–2100 averages, respectively) projections of global warming and global mean sea level rise from

8905-459: The best Paris climate agreement goal of 1.5 °C (2.7 °F). In that case, the likely range of sea level rise by 2100 is 28–55 cm (11– 21 + 1 ⁄ 2  in). The lowest scenario in AR5, RCP2.6, would see greenhouse gas emissions low enough to meet the goal of limiting warming by 2100 to 2 °C (3.6 °F). It shows sea level rise in 2100 of about 44 cm (17 in) with

9042-485: The best-case scenario, ice sheet under SSP1-2.6 gains enough mass by 2100 through surface mass balance feedbacks to reduce the sea levels by 2 cm (1 in). In the worst case, it adds 15 cm (6 in). For SSP5-8.5, the best-case scenario is adding 5 cm (2 in) to sea levels, and the worst-case is adding 23 cm (9 in). Greenland's peripheral glaciers and ice caps crossed an irreversible tipping point around 1997. Sea level rise from their loss

9179-459: The contribution from these is thought to be small. Glacier retreat and ocean expansion have dominated sea level rise since the start of the 20th century. Some of the losses from glaciers are offset when precipitation falls as snow, accumulates and over time forms glacial ice. If precipitation, surface processes and ice loss at the edge balance each other, sea level remains the same. Because of this precipitation began as water vapor evaporated from

9316-439: The country may face wet-bulb temperatures higher than humans and other mammals can tolerate more than six hours. Overall, the report identified 127 different negative impacts of climate change , some of them irreversible. People can protect themselves to some degree from the effects of climate change, which is known as adaptation . Overall, progress on adaptation has been made in all sectors and regions, although this progress

9453-528: The damage that is left behind – lives lost and livelihoods ruined. The question at this point is not whether we can altogether avoid the crisis – it is whether we can avoid the worst consequences." Swedish climate activist Greta Thunberg said that the Working Group 1 report "confirms what we already know from thousands [of] previous studies and reports – that we are in an emergency". Environmentalist Inger Andersen commented: "Nature can be our saviour ... but only if we save it first." In

9590-517: The differences. However, there can still be variations between the studies. In 2018, a systematic review estimated average annual ice loss of 43 billion tons (Gt) across the entire continent between 1992 and 2002. This tripled to an annual average of 220 Gt from 2012 to 2017. However, a 2021 analysis of data from four different research satellite systems ( Envisat , European Remote-Sensing Satellite , GRACE and GRACE-FO and ICESat ) indicated annual mass loss of only about 12 Gt from 2012 to 2016. This

9727-456: The distribution of sea water around the globe through gravity. Several approaches are used for sea level rise (SLR) projections. One is process-based modeling, where ice melting is computed through an ice-sheet model and rising sea temperature and expansion through a general circulation model , and then these contributions are added up. The so-called semi-empirical approach instead applies statistical techniques and basic physical modeling to

9864-399: The emissions of cities could be brought down to near zero, with the worst-case scenario assuming a non-mitigatable remainder of 3 GtCO 2 -eq. City planning, supporting mixed use of space, transit, walking, cycling and sharing vehicles can reduce urban emissions by 23–26%. Urban forests, lakes and other blue and green infrastructure can reduce emissions directly and indirectly (e.g. by reducing

10001-608: The emphasis on adaptation limits, the report also highlights loss and damage , meaning negative consequences of climate change that cannot be avoided through adaptation. The report states that such losses and damages are already widespread: droughts, floods and heatwaves are becoming more frequent, and a mass extinction is already underway. Taking near-term actions to limit warming to below 1.5 °C would substantially reduce future losses and damages, but cannot eliminate them all. Previously, rich countries have resisted taking responsibility for these losses. The report states that even

10138-428: The empirical 2.5 °C (4.5 °F) upper limit from ice cores. If temperatures reach or exceed that level, reducing the global temperature to 1.5 °C (2.7 °F) above pre-industrial levels or lower would prevent the loss of the entire ice sheet. One way to do this in theory would be large-scale carbon dioxide removal , but there would still be cause of greater ice losses and sea level rise from Greenland than if

10275-424: The energy demand for cooling). Buildings emitted 21% of global GHG emissions in the year 2019. 80–90% of their emissions can be cut while helping to achieve other Sustainable Development Goals . The report introduces a new scheme for reducing GHG emissions in buildings: SER = Sufficiency, Efficiency, Renewable. Sufficiency measures do not need very complex technology, energy supply, maintenance or replacement during

10412-517: The entire document was finalised at the 58th plenary meeting of the panel at Interlaken in March 2023 and was published on 20 March 2023. It includes a summary for policymakers and was the basis for the 2023 United Nations Climate Change Conference (COP28) in Dubai . In the report, there are guidelines for both responses in the near term and in the long-term. According to the report, the main source of

10549-403: The extremely low probability of large climate change-induced increases in precipitation greatly elevating ice sheet surface mass balance .) In 2020, 106 experts who contributed to 6 or more papers on sea level estimated median 118 cm ( 46 + 1 ⁄ 2  in) SLR in the year 2300 for the low-warming RCP2.6 scenario and the median of 329 cm ( 129 + 1 ⁄ 2  in) for

10686-559: The global mean sea level was rising by 3.2 mm ( 1 ⁄ 8  in) per year. This was double the average 20th century rate. The 2023 World Meteorological Organization report found further acceleration to 4.62 mm/yr over the 2013–2022 period. These observations help to check and verify predictions from climate change simulations. Regional differences are also visible in the tide gauge data. Some are caused by local sea level differences. Others are due to vertical land movements. In Europe , only some land areas are rising while

10823-617: The global temperature will rise by 1.5 degrees above pre-industrial levels, while if it will rise by more than 2 degrees it will become impossible "in some regions and sub-regions". Although the report's outlook is bleak, its conclusion argues that there is still time to limit warming to 1.5 °C (2.7 °F) by drastic cuts to greenhouse gas emission , but such action must be taken immediately. Moreover, climate resilient development can have both adaptation and mitigation benefits, but it requires international cooperation and collaborations with local communities and organisations. The report

10960-1034: The greatest exposure to sea level rise, twelve are in Asia , including Indonesia , Bangladesh and the Philippines. The resilience and adaptive capacity of ecosystems and countries also varies, which will result in more or less pronounced impacts. The greatest impact on human populations in the near term will occur in the low-lying Caribbean and Pacific islands . Sea level rise will make many of them uninhabitable later this century. Societies can adapt to sea level rise in multiple ways. Managed retreat , accommodating coastal change , or protecting against sea level rise through hard-construction practices like seawalls are hard approaches. There are also soft approaches such as dune rehabilitation and beach nourishment . Sometimes these adaptation strategies go hand in hand. At other times choices must be made among different strategies. Poorer nations may also struggle to implement

11097-536: The high-warming RCP8.5. The former scenario had the 5%–95% confidence range of 24–311 cm ( 9 + 1 ⁄ 2 – 122 + 1 ⁄ 2  in), and the latter of 88–783 cm ( 34 + 1 ⁄ 2 – 308 + 1 ⁄ 2  in). After 500 years, sea level rise from thermal expansion alone may have reached only half of its eventual level - likely within ranges of 0.5–2 m ( 1 + 1 ⁄ 2 – 6 + 1 ⁄ 2  ft). Additionally, tipping points of Greenland and Antarctica ice sheets are likely to play

11234-417: The hypothesis after 2016 often suggested that the ice shelves in the real world may collapse too slowly to make this scenario relevant, or that ice mélange - debris produced as the glacier breaks down - would quickly build up in front of the glacier and significantly slow or even outright stop the instability soon after it began. Due to these uncertainties, some scientists - including the originators of

11371-543: The hypothesis, Robert DeConto and David Pollard - have suggested that the best way to resolve the question would be to precisely determine sea level rise during the Last Interglacial . MICI can be effectively ruled out if SLR at the time was lower than 4 m (13 ft), while it is very likely if the SLR was greater than 6 m ( 19 + 1 ⁄ 2  ft). As of 2023, the most recent analysis indicates that

11508-415: The ice and oceans factor in ongoing deformations of the solid Earth . They look in particular at landmasses still rising from past ice masses retreating , and the Earth's gravity and rotation . Since the launch of TOPEX/Poseidon in 1992, an overlapping series of altimetric satellites has been continuously recording the sea level and its changes. These satellites can measure the hills and valleys in

11645-408: The ice on Earth would result in about 70 m (229 ft 8 in) of sea level rise, although this would require at least 10,000 years and up to 10 °C (18 °F) of global warming. The oceans store more than 90% of the extra heat added to the climate system by Earth's energy imbalance and act as a buffer against its effects. This means that the same amount of heat that would increase

11782-401: The increase in global warming is due to the increase in CO 2 emissions, stating that it is likely or very likely to exceed 1.5 °C under higher emission scenarios. The panel published a longer report, a summary for policymakers a presentation and a short "Headline Statements" document. Some key example headline statements include: Sea level rise Between 1901 and 2018,

11919-735: The largest potential source of sea level rise. However the West Antarctic ice sheet (WAIS) is substantially more vulnerable. Temperatures on West Antarctica have increased significantly, unlike East Antarctica and the Antarctic Peninsula . The trend is between 0.08 °C (0.14 °F) and 0.96 °C (1.73 °F) per decade between 1976 and 2012. Satellite observations recorded a substantial increase in WAIS melting from 1992 to 2017. This resulted in 7.6 ± 3.9 mm ( 19 ⁄ 64  ±  5 ⁄ 32  in) of Antarctica sea level rise. Outflow glaciers in

12056-414: The last million years, during which the temperatures have at most been 2.5 °C (4.5 °F) warmer than the preindustrial average. 2012 modelling suggested that the tipping point of the ice sheet was between 0.8 °C (1.4 °F) and 3.2 °C (5.8 °F). 2023 modelling has narrowed the tipping threshold to a 1.7 °C (3.1 °F)-2.3 °C (4.1 °F) range, which is consistent with

12193-429: The late 21st century. According to a 2021 study in which plausible AR5 and RCP scenarios of CO 2 emissions are selected, Across all RCPs, global mean sea level is projected to rise by 0.26 to 0.82 m by the late 21st century. The IPCC Fifth Assessment Report also projected changes in climate beyond the 21st century. The extended RCP2.6 pathway assumes sustained net negative anthropogenic GHG emissions after

12330-407: The life of the building. Those include, natural ventilation, green roofs, white walls, mixed use of spaces, collective use of devices etc. Reducing GHG emissions from buildings is linked to sharing economy and circular economy . The IPCC found that decent living standards could be achieved using less energy than prior consensus assumed. According to the report for reaching well being for all,

12467-426: The majority of the ice sheet, which is located below the sea level. Its collapse would cause ~3.3 m (10 ft 10 in) of sea level rise. This disappearance would take an estimated 2000 years. The absolute minimum for the loss of West Antarctica ice is 500 years, and the potential maximum is 13,000 years. Once ice loss from the West Antarctica is triggered, the only way to restore it to near-present values

12604-443: The melting of Greenland ice sheet would most likely add around 6 cm ( 2 + 1 ⁄ 2  in) to sea levels under the low-emission scenario, and 13 cm (5 in) under the high-emission scenario. The first scenario, SSP1-2.6 , largely fulfils the Paris Agreement goals, while the other, SSP5-8.5, has the emissions accelerate throughout the century. The uncertainty about ice sheet dynamics can affect both pathways. In

12741-547: The middle of the 21st century. However, Joeri Rogelj , director of the Grantham Institute and a lead IPCC author, said that it is possible to completely avoid warming of 1.5 °C, but to achieve that the world would need to cut emissions by 50% by the year 2030 and by 100% by the year 2050. If the world does not begin to drastically cut emissions by the time of the next report of the IPCC, then it will no longer be possible to prevent 1.5 °C of warming. SSP1-1.9

12878-413: The models used for writing the report, with the lived experience proving more severe than the consensus science . After publication of the Working Group 1 report, EU Vice President Frans Timmermans said that it is not too late to prevent runaway climate change . UK Prime Minister Boris Johnson said that the next decade will be pivotal to the future of the planet. Rick Spinrad , administrator of

13015-568: The most expensive projects ever attempted. Most ice on Greenland is in the Greenland ice sheet which is 3 km (10,000 ft) at its thickest. The rest of Greenland ice forms isolated glaciers and ice caps. The average annual ice loss in Greenland more than doubled in the early 21st century compared to the 20th century. Its contribution to sea level rise correspondingly increased from 0.07 mm per year between 1992 and 1997 to 0.68 mm per year between 2012 and 2017. Total ice loss from

13152-628: The observed ice-sheet erosion in Greenland and Antarctica had matched the upper-end range of the AR5 projections by 2020, and the finding that AR5 projections were likely too slow next to an extrapolation of observed sea level rise trends, while the subsequent reports had improved in this regard. Further, AR5 was criticized by multiple researchers for excluding detailed estimates the impact of "low-confidence" processes like marine ice sheet and marine ice cliff instability, which can substantially accelerate ice loss to potentially add "tens of centimeters" to sea level rise within this century. AR6 includes

13289-506: The observed sea level rise and its reconstructions from the historical geological data (known as paleoclimate modeling). It was developed because process-based model projections in the past IPCC reports (such as the Fourth Assessment Report from 2007) were found to underestimate the already observed sea level rise. By 2013, improvements in modeling had addressed this issue, and model and semi-empirical projections for

13426-403: The occurrence of extreme weather events. Even in a 1.5 °C temperature rise there will be "an increasing occurrence of some extreme events unprecedented in the observational record". The likelihood of more rare events increases more. The frequency, and the intensity of such events will considerably increase with warming, as described in the following table: The second part of the report,

13563-473: The ocean gains heat, the water expands and sea level rises. Warmer water and water under great pressure (due to depth) expand more than cooler water and water under less pressure. Consequently, cold Arctic Ocean water will expand less than warm tropical water. Different climate models present slightly different patterns of ocean heating. So their projections do not agree fully on how much ocean heating contributes to sea level rise. The large volume of ice on

13700-543: The ocean surface, effects of climate change on the water cycle can even increase ice build-up. However, this effect is not enough to fully offset ice losses, and sea level rise continues to accelerate. The contributions of the two large ice sheets, in Greenland and Antarctica , are likely to increase in the 21st century. They store most of the land ice (~99.5%) and have a sea-level equivalent (SLE) of 7.4 m (24 ft 3 in) for Greenland and 58.3 m (191 ft 3 in) for Antarctica. Thus, melting of all

13837-401: The other hand, the whole EAIS would not definitely collapse until global warming reaches 7.5 °C (13.5 °F), with a range between 5 °C (9.0 °F) and 10 °C (18 °F). It would take at least 10,000 years to disappear. Some scientists have estimated that warming would have to reach at least 6 °C (11 °F) to melt two thirds of its volume. East Antarctica contains

13974-454: The others are sinking. Since 1970, most tidal stations have measured higher seas. However sea levels along the northern Baltic Sea have dropped due to post-glacial rebound . An understanding of past sea level is an important guide to where current changes in sea level will end up. In the recent geological past, thermal expansion from increased temperatures and changes in land ice are the dominant reasons of sea level rise. The last time that

14111-651: The poorly observed areas. A more complete observational record shows continued mass gain. In spite of the net mass gain, some East Antarctica glaciers have lost ice in recent decades due to ocean warming and declining structural support from the local sea ice , such as Denman Glacier , and Totten Glacier . Totten Glacier is particularly important because it stabilizes the Aurora Subglacial Basin . Subglacial basins like Aurora and Wilkes Basin are major ice reservoirs together holding as much ice as all of West Antarctica. They are more vulnerable than

14248-556: The preindustrial levels. Since the Last Glacial Maximum , about 20,000 years ago, sea level has risen by more than 125 metres (410 ft). Rates vary from less than 1 mm/year during the pre-industrial era to 40+ mm/year when major ice sheets over Canada and Eurasia melted. Meltwater pulses are periods of fast sea level rise caused by the rapid disintegration of these ice sheets. The rate of sea level rise started to slow down about 8,200 years before today. Sea level

14385-507: The projected range for total sea level rise was 9.5–16.2 metres (31–53 ft) by the year 2300. Projections for subsequent years are more difficult. In 2019, when 22 experts on ice sheets were asked to estimate 2200 and 2300 SLR under the 5   °C warming scenario, there were 90% confidence intervals of −10 cm (4 in) to 740 cm ( 24 + 1 ⁄ 2  ft) and − 9 cm ( 3 + 1 ⁄ 2  in) to 970 cm (32 ft), respectively. (Negative values represent

14522-538: The publication of results from the Sixth Assessment Report. The sixth assessment report is made up of the reports of three working groups (WG I, II, and III) and a synthesis report which concluded the assessment in early 2023. Geopolitics has been included in climate models for the first time, in the form of five Shared Socioeconomic Pathways : SSP1 "Taking the Green Road", SSP2 "Middle of

14659-408: The radiative forcing reached by 2100 Projections for temperature according to RCP 6.0 include continuous global warming through 2100 where CO 2 levels rise to 670 ppm by 2100 making the global temperature rise by about 3–4 °C by 2100. RCP7 is a baseline outcome rather than a mitigation target. In RCP 8.5 emissions continue to rise throughout the 21st century. RCP8.5 is generally taken as

14796-696: The rate of deforestation slowed after 2010 and the total forest cover increased in the latest years due to reforestation in Europe, Asia and North America. The publication of the Working Group 1 report in 2021 was during the Northern Hemisphere summer, where there was much extreme weather, such as a Western North America heat wave , flooding in Europe , extreme rainfall in India and China , and wildfires in several countries. Some scientists are describing these extreme weather events as clear gaps in

14933-1316: The report demand side mitigation measures can reduce GHG emissions by 40–70% by the year 2050 compared to scenarios in which countries will fulfill its national pledges given before 2020. For being implemented successfully those measures should be linked "with improving basic wellbeing for all". The report concluded that in order to achieve net zero emissions, it is necessary to employ carbon dioxide removal technologies, stating "All global pathways that limit warming to 1.5 °C ... with no or limited overshoot, and those that limit warming to 2 °C... involve rapid and deep and in most cases immediate GHG emission reductions in all sectors. Modelled mitigation strategies to achieve these reductions include transitioning from fossil fuels without CCS to very low- or zero-carbon energy sources, such as renewables or fossil fuels with CCS, demand side measures and improving efficiency, reducing non-CO 2 emissions, and deploying carbon dioxide removal (CDR) methods to counterbalance residual GHG emissions". The report compares different methods of carbon dioxide removal (CDR) including agroforestry , reforestation , blue carbon management, restoration of peatland and others. Cities have great potential for reducing greenhouse gas emissions. With full scale mitigation action

15070-516: The report, described this finding as one of the most radical, debunking a common refrain by energy poverty advocates, that development requires use of fossil fuels. The Secretary-General of the UN , António Guterres , called the report of Working Group 1 a " code red for humanity ". Responding to the Working Group 2 report, he called it "an atlas of human suffering and a damning indictment of failed climate leadership" and "the facts are undeniable ...

15207-726: The required energy consumption is "between 20 and 50 GJ cap-1 yr-1 depending on context." More equitable income distribution can lower emissions. Mitigation pathways based on low demand and high efficiency can achieve decent living standards and well being for all. Pathways based on reducing consumption, involving sustainable development have less negative outcomes than pathways based on high consumption and narrow mitigation. According to table TS30, narrow mitigation can increase habitat loss by 600%, while avoiding habitat degradation by around 95%. Mitigation with sustainable development did not harm forest cover and biodiversity. The report mentions some improvement in global climate action. For example,

15344-563: The rest of East Antarctica. Their collective tipping point probably lies at around 3 °C (5.4 °F) of global warming. It may be as high as 6 °C (11 °F) or as low as 2 °C (3.6 °F). Once this tipping point is crossed, the collapse of these subglacial basins could take place over as little as 500 or as much as 10,000 years. The median timeline is 2000 years. Depending on how many subglacial basins are vulnerable, this causes sea level rise of between 1.4 m (4 ft 7 in) and 6.4 m (21 ft 0 in). On

15481-466: The risk of infectious diseases outbreaks like the COVID-19 pandemic . The report also cites evidence that China will pay the highest financial cost if the temperature continue to rise. The impacts will include food insecurity, water scarcity, flooding, especially in coastal areas where most of the population lives due to higher than average sea level rise, and more powerful cyclones. At some point part of

15618-458: The same approaches to adapt to sea level rise as richer states. Between 1901 and 2018, the global mean sea level rose by about 20 cm (7.9 in). More precise data gathered from satellite radar measurements found an increase of 7.5 cm (3.0 in) from 1993 to 2017 (average of 2.9 mm (0.11 in)/yr). This accelerated to 4.62 mm (0.182 in)/yr for 2013–2022. Paleoclimate data shows that this rate of sea level rise

15755-403: The same assessment cycle: A total of 234 scientists from 66 countries contributed to the first of three working group reports. Working group 1 (WGI) published Climate Change 2021: The Physical Science Basis . The report's authors built on more than 14,000 scientific papers to produce a 3,949-page report, which was then approved by 195 governments. The Summary for Policymakers (SPM) document

15892-537: The same time improving sustainability. The report further highlighted the need for conservation in order to maintain biodiversity , and mitigate the effects of climate change. The report reads, "Recent analyses, drawing on a range of lines of evidence, suggest that maintaining the resilience of biodiversity and ecosystem services at a global scale depends on effective and equitable conservation of approximately 30% to 50% of Earth's land, freshwater and ocean areas, including currently near-natural ecosystems." The report

16029-426: The same. The same estimate found that if the temperature stabilized below 2 °C (3.6 °F), 2300 sea level rise would still exceed 1.5 m (5 ft). Early net zero and slowly falling temperatures could limit it to 70–120 cm ( 27 + 1 ⁄ 2 –47 in). By 2021, the IPCC Sixth Assessment Report was able to provide estimates for sea level rise in 2150. Keeping warming to 1.5   °C under

16166-404: The sea caused by currents and detect trends in their height. To measure the distance to the sea surface, the satellites send a microwave pulse towards Earth and record the time it takes to return after reflecting off the ocean's surface. Microwave radiometers correct the additional delay caused by water vapor in the atmosphere . Combining these data with the location of the spacecraft determines

16303-476: The sea-surface height to within a few centimetres. These satellite measurements have estimated rates of sea level rise for 1993–2017 at 3.0 ± 0.4 millimetres ( 1 ⁄ 8  ±  1 ⁄ 64  in) per year. Satellites are useful for measuring regional variations in sea level. An example is the substantial rise between 1993 and 2012 in the western tropical Pacific. This sharp rise has been linked to increasing trade winds . These occur when

16440-423: The solution. It states that "International cooperation is a critical enabler for achieving ambitious climate change mitigation goals." For preventing global temperature from rising more than 2 degrees above the preindustrial level, international cooperation needs to be much stronger than now as many developing countries need support from other countries higher than present for strong climate action. According to

16577-673: The specific regions. A structured expert judgement may be used in combination with modeling to determine which outcomes are more or less likely, which is known as "shifted SEJ". Semi-empirical techniques can be combined with the so-called "intermediate-complexity" models. After 2016, some ice sheet modeling exhibited the so-called ice cliff instability in Antarctica, which results in substantially faster disintegration and retreat than otherwise simulated. The differences are limited with low warming, but at higher warming levels, ice cliff instability predicts far greater sea level rise than any other approach. The Intergovernmental Panel on Climate Change

16714-453: The total sea level rise in his scenario would be in the range of 0.98–4.82 m (3–16 ft) by 2150. AR6 also provided lower-confidence estimates for year 2300 sea level rise under SSP1-2.6 and SSP5-8.5 with various impact assumptions. In the best case scenario, under SSP1-2.6 with no ice sheet acceleration after 2100, the estimate was only 0.8–2.0 metres (2.6–6.6 ft). In the worst estimated scenario, SSP-8.5 with ice cliff instability,

16851-671: The war not to overshadow the WGII report. The report found that climate impacts are at the high end of previous estimates, with all parts of the world being affected. At least 3.3 billion people, about 40% of the world population , now fall into the most serious category of "highly vulnerable", with the worst effects in the developing world . If emissions continue on their current path, Africa will lose 30% of its maize cultivation territory and 50% of its land cultivated for beans . One billion people face flooding due to sea level rise . Climate change, together with other factors, also increases

16988-445: The water melts more and more of their height as their retreat continues, thus accelerating their breakdown on its own. This is widely accepted, but is difficult to model. The latter posits that coastal ice cliffs which exceed ~ 90 m ( 295 + 1 ⁄ 2  ft) in above-ground height and are ~ 800 m ( 2,624 + 1 ⁄ 2  ft) in basal (underground) height are likely to rapidly collapse under their own weight once

17125-476: The whole world to be net zero before 2050. Staying within this budget, if counting from the beginning of the year 2020, gives a 50% chance to stay below 1.5 °C. For having a 67% chance, the budget is 400 billion tonnes and for an 83% chance it is 300 billion tonnes. The report says that rapidly reducing methane emissions is very important, to make short-term gains to buy time for carbon dioxide emission cuts to take effect. Any future warming will increase

17262-448: The world's biggest polluters are guilty of arson of our only home." He also said that the report of Working Group 3 described "litany of broken climate promises [by policy makers]" and in his remarks called for more action, saying "Climate activists are sometimes depicted as dangerous radicals. But, the truly dangerous radicals are the countries that are increasing the production of fossil fuels." The synthesis report which summarises

17399-556: The year 2000. The Thwaites Glacier now accounts for 4% of global sea level rise. It could start to lose even more ice if the Thwaites Ice Shelf fails and would no longer stabilize it, which could potentially occur in mid-2020s. A combination of ice sheet instability with other important but hard-to-model processes like hydrofracturing (meltwater collects atop the ice sheet, pools into fractures and forces them open) or smaller-scale changes in ocean circulation could cause

17536-413: The year 2070. Negative emissions means that in total, humans absorb more GHGs from the atmosphere than they release. The extended RCP8.5 pathway assumes continued anthropogenic GHG emissions after 2100. In the extended RCP 2.6 pathway, atmospheric CO 2 concentrations reach around 360 ppmv by 2300, while in the extended RCP8.5 pathway, CO 2 concentrations reach around 2000 ppmv in 2250, which

17673-594: The year 2100 are now very similar. Yet, semi-empirical estimates are reliant on the quality of available observations and struggle to represent non-linearities, while processes without enough available information about them cannot be modeled. Thus, another approach is to combine the opinions of a large number of scientists in what is known as a structured expert judgement (SEJ). Variations of these primary approaches exist. For instance, large climate models are always in demand, so less complex models are often used in their place for simpler tasks like projecting flood risk in

17810-450: Was almost constant for the last 2,500 years. The recent trend of rising sea level started at the end of the 19th or beginning of the 20th century. The three main reasons why global warming causes sea levels to rise are the expansion of oceans due to heating , water inflow from melting ice sheets and water inflow from glaciers. Other factors affecting sea level rise include changes in snow mass, and flow from terrestrial water storage, though

17947-407: Was considered even more important than the 2014 IPCC Fifth Assessment Report . Even more rapid sea level rise was proposed in a 2016 study led by Jim Hansen , which hypothesized multi-meter sea level rise in 50–100 years as a plausible outcome of high emissions, but it remains a minority view amongst the scientific community. Marine ice cliff instability had also been very controversial, since it

18084-458: Was critical of technological approaches to carbon dioxide removal , instead indicating that urbanisation could help drive adoption of mitigation strategies such as public transport and renewable energy . The report also warns there are high risks associated with strategies such as solar radiation management ; planting forests in unnatural locations; or "poorly implemented bioenergy, with or without carbon capture and storage ". In line with

18221-491: Was drafted by scientists and agreed to line-by-line by the 195 governments in the IPCC during the five days leading up to 6 August 2021. It was published on Monday, 9 August 2021. According to the report, it is only possible to avoid warming of 1.5 °C or 2 °C if massive and immediate cuts in greenhouse gas emissions are made. In a front-page story, The Guardian described the report as "its starkest warning yet" of "major inevitable and irreversible climate changes",

18358-509: Was due to greater ice gain in East Antarctica than estimated earlier. In the future, it is known that West Antarctica at least will continue to lose mass, and the likely future losses of sea ice and ice shelves , which block warmer currents from direct contact with the ice sheet, can accelerate declines even in East Antarctica. Altogether, Antarctica is the source of the largest uncertainty for future sea level projections. In 2019,

18495-461: Was finished in March 2023. It includes a summary for policymakers and was the basis for the 2023 United Nations Climate Change Conference (COP28) in Dubai . The first of the three working groups published its report on 9 August 2021, Climate Change 2021: The Physical Science Basis . A total of 234 scientists from 66 countries contributed to this first working group (WGI) report. The authors built on more than 14,000 scientific papers to produce

18632-414: Was presented on 4 April 2022. Some observers are worried that the conclusions might be watered down, considering the way the reports are adopted. According to The Observer , some countries "have sought to make changes that would weaken the final warnings". The report uses some new approaches like to include different social aspects, the participation of youth , indigenous people , cities, businesses in

18769-472: Was proposed as a modelling exercise, and the observational evidence from both the past and the present is very limited and ambiguous. So far, only one episode of seabed gouging by ice from the Younger Dryas period appears truly consistent with this theory, but it had lasted for an estimated 900 years, so it is unclear if it supports rapid sea level rise in the present. Modelling which investigated

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