The latest report by the Intergovernmental Panel on Climate Change (IPCC), released today is warning that climate change is widespread, rapid - and intensifying - with sea level rise of up to half a meter "irreversible." 

According to the report, past, present and future emissions of CO2 commit the world to substantial multi-century climate change, and many aspects of climate change would persist for centuries even if emissions of CO2 were stopped immediately.

A large fraction of this change is "essentially irreversible on a multi-century to millennial time scale, barring large net removal (‘negative emissions’) of CO2 from the atmosphere over a sustained period through as yet unavailable technological means."

"Instability...resulting in multi metre rise in sea level ..could be triggered at 1.5°C to 2°C of global warming"

Other extracts from the report - IPCC Working Group I report, Climate Change 2021: the Physical Science Basis - make for similarly grim reading:

"Changes are irreversible on centennial to millennial time scales in global ocean temperature (very high confidence), deep ocean acidification (very high confidence) and deoxygenation (medium confidence).

"Mountain and polar glaciers are committed to continue melting for decades or centuries (very high confidence). Loss of permafrost carbon following permafrost thaw is irreversible at centennial timescales (high confidence). Continued ice loss over the 21st century is virtually certain for the Greenland Ice Sheet and likely for the Antarctic Ice Sheet." ......

"Continued GHG emissions greatly increase the likelihood of potentially irreversible changes in the global climate system, in particular with respect to the contribution of ice sheets to global sea level change (high confidence)."

"Over the past four to six decades, it is virtually certain that the global ocean has warmed, with human influence extremely likely the main driver since the 1970s, making climate change irreversible over centuries to millennia (medium confidence)."

"... global-scale glacier mass loss, permafrost thaw, and decline in snow cover and Arctic sea ice extent will continue in the near term (2031–2050) due to surface air temperature increases (high confidence). The Greenland and Antarctic Ice Sheets are projected to lose mass at an increasing rate throughout the 21st century and beyond (high confidence).

"Sea level rise will also continue at an increasing rate.…..Extreme sea level events that occurred once per hundred years in the recent past are projected to occur at least once per year at many locations by 2050, especially in tropical regions, under all RCP scenarios (high confidence).

"However, instability and/or irreversible loss of the Greenland and Antarctic Ice Sheets, resulting in multi metre rise in sea level over hundreds to thousands of years, could be triggered at 1.5°C to 2°C of global warming (medium confidence)."

"Strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change"

Scientists worldwide are observing changes in the Earth’s climate in every region and across the whole climate system.

Many of the changes observed in the climate are unprecedented in thousands, if not hundreds of thousands of years, and some of the changes already set in motion—such as continued sea level rise—are irreversible over hundreds to thousands of years.

However, strong and sustained reductions in emissions of carbon dioxide (CO2) and other greenhouse gases would limit climate change, although it could take 20-30 years to see global temperatures stabilize, according to the  report, which is the first instalment of the IPCC’s Sixth Assessment Report (AR6), which will be completed in 2022.

The start warning from the IPCC says that world will continue to get hotter and wetter and extreme weather events will become more frequent. Many of the impacts are already "baked in" -for example, sea level rise will continue for centuries, if not for thousands of years, even if we manage to stabilise global temperatures. 

“This report reflects extraordinary efforts under exceptional circumstances,” said Hoesung Lee, Chair of the IPCC. “The innovations in this report, and advances in climate science that it reflects, provide an invaluable input into climate negotiations and decision-making.”

Without immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will be beyond reach

The report provides new estimates of the chances of crossing the global warming level of 1.5°C in the next decades, and finds that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C or even 2°C will be beyond reach.

The report shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1°C of warming since 1850-1900, and finds that averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C of warming.

The assessment is based on improved observational datasets to assess historical warming, as well progress in scientific understanding of the response of the climate system to human-caused greenhouse gas emissions.

“This report is a reality check,” said IPCC Working Group I Co-Chair Valérie Masson-Delmotte. “We now have a much clearer picture of the past, present and future climate, which is essential for understanding where we are headed, what can be done, and how we can prepare.”

Every region facing increasing changes

Many characteristics of climate change directly depend on the level of global warming, but what people experience is often very different to the global average. For example, warming over land is larger than the global average, and it is more than twice as high in the Arctic.

“Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming,” said IPCC Working Group I Co-Chair Panmao Zhai.

The report projects that in the coming decades climate changes will increase in all regions. For 1.5°C of global warming, there will be increasing heat waves, longer warm seasons and shorter cold seasons.

At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the report shows.

In addition to temperature change, the report shows that climate change is bringing multiple different changes in different regions – which will all increase with further warming. These include changes to wetness and dryness, to winds, snow and ice, coastal areas and oceans. For example:

• Climate change is intensifying the water cycle. This brings more intense rainfall and associated flooding, as well as more intense drought in many regions.
• Climate change is affecting rainfall patterns. In high latitudes, precipitation is likely to increase, while it is projected to decrease over large parts of the subtropics. Changes to monsoon precipitation are expected, which will vary by region.
• Coastal areas will see continued sea level rise throughout the 21st century, contributing to more frequent and severe coastal flooding in low-lying areas and coastal erosion. Extreme sea level events that previously occurred once in 100 years could happen every year by the end of this century.
• Further warming will amplify permafrost thawing, and the loss of seasonal snow cover, melting of glaciers and ice sheets, and loss of summer Arctic sea ice.
• Changes to the ocean, including warming, more frequent marine heatwaves, ocean acidification, and reduced oxygen levels have been clearly linked to human influence. These changes affect both ocean ecosystems and the people that rely on them, and they will continue throughout at least the rest of this century.
• For cities, some aspects of climate change may be amplified, including heat (since urban areas are usually warmer than their surroundings), flooding from heavy precipitation events and sea level rise in coastal cities.

For the first time, the Sixth Assessment Report provides a more detailed regional assessment of climate change, including a focus on useful information that can inform risk assessment, adaptation, and other decision-making, and a new framework that helps translate physical changes in the climate – heat, cold, rain, drought, snow, wind, coastal flooding and more – into what they mean for society and ecosystems.

The regional information can be explored in detail in the newly developed Interactive Atlas interactive-atlas.ipcc.ch as well as regional fact sheets and the technical summary.

The report is also accompanied by a a separate 40 page Summary for Policymakers paper.

Human influence on the past and future climate

“It has been clear for decades that the Earth’s climate is changing, and the role of human influence on the climate system is undisputed,” said Masson-Delmotte.

The report also shows that human actions still have the potential to determine the future course of climate. The evidence is clear that carbon dioxide (CO2) is the main driver of climate change, even as other greenhouse gases and air pollutants also affect the climate.

“Stabilizing the climate will require strong, rapid, and sustained reductions in greenhouse gas emissions, and reaching net zero CO2 emissions. Limiting other greenhouse gases and air pollutants, especially methane, could have benefits both for health and the climate,” said Zhai.

The 3949 page report has been prepared by 234 authors from 66 countries, together with 517 contributing authors, over 14,000 cited references and a total of 78,007 expert and government review comments.

Click here to download the full report Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change

Click here to download the Summary for Policymakers of the Working Group I contribution to the Sixth Assessment Report (AR6).

Click here to watch the IPCC Press Conference present the findings of the report on the WaterBriefing Watch channel