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Climate change is here and some of its effects will stick around for centuries; but if humanity immediately and rapidly reduces worldwide carbon dioxide and other greenhouse gas emissions, some of these irreversible changes can be slowed, a major new scientific report from the UN has concluded.
The report, from the Intergovernmental Panel on Climate Change (IPCC), shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1 degrees Celsius of warming since the period of 1850 to 1900 and finds that, over the next 20 years, global temperature is expected to reach or exceed 1.5 degrees of warming.
The report projects that in the coming decades climate change will increase in all regions. There will be increasing heat waves, longer warm seasons and shorter cold seasons. At 2 degrees of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and human health.
“This report reaffirms that there is a near linear relationship between the cumulative amount of emissions of carbon dioxide in the atmosphere from human activities and the extent of observed and future warming. This is physics,” said the report’s co-chair Valérie Masson-Delmotte in a virtual press conference on Monday. “This means that the only way to limit global warming is to reach net-zero carbon dioxide emissions at the global scale.”
The report highlights the status of major climate change indicators. Levels of heat-trapping gases in the atmosphere have continued to rapidly increase. Current carbon dioxide concentrations are the highest they have been in at least 2 million years. Over the past 100 years, sea level has risen at the fastest rates observed in at least 3,000 years. Artic sea ice area is at its lowest level in at least 1,000 years. Finally, the retreat of glaciers on a global scale has been unprecedented for at least the last 2,000 years.
“This report is a reality check,” Masson-Delmotte added. “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.”
Increasing changes observed in every region
“Climate change is already affecting every region on Earth, in multiple ways.” said Panmao Zhai, the report’s co-chair. “The changes we experience will increase with additional warming,”
The report details changes to wetness and dryness, 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, 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 might 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.
The report provides detailed regional assessments of climate change, including a focus on useful information that can inform risk assessment, adaptation and other decision-making. It also offers a new framework to help translate physical changes in the climate – heat, cold, rain, drought, snow, wind, coastal flooding and more – into what they mean for society and ecosystems.
This regional information can be explored in detail in the newly developed Interactive Atlas as well as regional fact sheets, the technical summary, and underlying report.
Longer-term changes for slow processes
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 – will take that same amount of time to be reversed, according to the report.
“Changes in ice sheets, deep ocean temperature, and acidification will continue for centuries to thousands of years, meaning that they are irreversible in our lifetime and will continue for generations to come,” said Masson-Delmotte.
Helene Hewitt, coordinating author for the chapter on ocean, cryosphere and sea level change, explained in a phone interview that these parts of the climate system are slow processes, and even if we succeed in limiting carbon dioxide and greenhouse gas emissions to net-zero, it would take centuries to reverse the changes that are already happening now.
With strong reductions to emissions, we would immediately get improved air quality. But other changes would not come as quickly; it could take 20 to 30 years for global temperatures to stabilize, according to the report.
In the press conference Petteri Taalas, secretary general of the World Meteorological Organization, emphasized the climate’s link to recent extreme events, such as forest fires on the West Coast of the U.S. and severe flooding in Central Europe and China.
“[At the] UN, our aim is 1.5 degrees, which will be best for mankind. Now we are heading toward 2 to 3 degrees of warming instead,” he said. “This is not enough to avoid several harmful impacts like loss of food production capacity, extreme heat, forest fires, continued sea level rise, potential refugee crises, and negative impacts on the world economy and biosphere.”
Talaas urged world leaders to “pay attention to climate adaptation since the negative trend in climate would continue for decades and, in some cases, for thousands of years.”
“Governments need to make their net-zero plan an integral part of their Paris Commitments. They must finance and support developing countries to adapt to climate change as promised under the Paris Agreement. They must decarbonize faster,” said Inger Andersen, executive director of UN Environment. “They must restore natural systems and draw down carbon, cut out methane and other greenhouse gasses faster. [They must] get behind the Kigali Amendment to the Montreal Protocol to cut the climate impact of the cooling industry. And every business, every investor and every citizen needs to play their part.”
The new IPCC report puts pressure on countries attending the annual UN climate change conference in early November (COP26) to adjust their emissions reductions goals to meet the 2015 Paris Climate Agreement to keep global temperatures well below 2 degrees compared to pre-industrial levels. The treaty aims to reach global peaking of greenhouse gas emissions as soon as possible to achieve a climate neutral world by mid-century.