Climate change is widespread, rapid, and intensifying, according to a major new report by the Intergovernmental Panel on Climate Change (IPCC).
It is unequivocal that human influence has warmed the atmosphere, ocean and land, the report’s authors state. “Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred,” they added.
“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.”
The report comes as wildfires rage in several countries in Europe, and in British Colombia in Canada, California in the US, and parts of Siberia in Russia. Numerous areas in the world have been suffering devastating floods.
The new IPCC report states that human-induced climate change is already affecting many weather and climate extremes in every region across the globe. “Evidence of observed changes in extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, and, in particular, their attribution to human influence, has strengthened since the Fifth Assessment Report,” it says.
It projects that, in the coming decades, climate changes will increase in all regions. For 1.5°C of global warming, there would be increasing heat waves, longer warm seasons, and shorter cold seasons, the report states.
At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, it adds.
“Global surface temperature will continue to increase until at least the mid-century under all emissions scenarios considered,” the report states. “Global warming of 1.5°C and 2°C will be exceeded during the 21st century unless deep reductions in CO2 and other greenhouse gas emissions occur in the coming decades.”
Since 1970, the global surface temperature has increased faster than in any other 50-year period over at least the past 2,000 years, the report adds.
While strong and sustained reductions in emissions of carbon dioxide and other greenhouse gases would limit climate change, and benefits for air quality would come quickly, it could take twenty to thirty years to see global temperatures stabilise, the report states.
The report also says that a rise in sea levels of close to two metres by the end of this century cannot be ruled out.
It adds that the global mean sea level has risen faster since 1900 than over any preceding century in at least the past 3,000 years and the global ocean has warmed faster over the past century than since the end of the last deglacial transition (about 11,000 years ago).
The UN secretary-general, Antonio Guterres, said the IPCC’s assessment was “code red for humanity”. He tweeted: “The internationally agreed threshold of 1.5°C global warming is perilously close. We must step up our efforts and act urgently & decisively to keep the 1.5°C target alive.”
He added: ” The evidence is irrefutable: greenhouse gas emissions are choking our planet & placing billions of people in danger. Global heating is affecting every region on Earth, with many of the changes becoming irreversible. We must act decisively now to avert a climate catastrophe.”
The new Working Group 1 report, entitled ‘Climate Change 2021: the Physical Science Basis’, is the first instalment of the IPCC’s Sixth Assessment Report, which will be completed in 2022.
The report, which was co-written by 234 authors from 66 countries, was approved on August 6 by 195 member governments.
It was the first time that the IPCC conducted its approval session virtually. The session was held over two weeks and involved a record 739 participants.
Working Group 2 will look at impacts, adaptation, and vulnerability and Working Group 3 will examine mitigation. A synthesis report will then integrate the three working group reports as well as the findings from the three cross-working group special reports prepared during the current assessment cycle.
The new report says that emissions of greenhouse gases from human activities have been responsible for approximately 1.1°C of warming since 1850–1900. It says the evidence is clear that, while other greenhouse gases and air pollutants also affect the climate, carbon dioxide is the main driver of climate change.
The report predicts changes to wetness and dryness, to winds, to snow and ice, and to coastal areas and oceans.
It gives the following examples:
- 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 a continued rise in sea levels 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, the melting of glaciers and ice sheets, and the loss of summer Arctic sea ice. (The report says the Arctic is likely to be practically free of sea ice in September at least once before 2050.)
- 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.
- In cities, some aspects of climate change may be amplified, including heat (urban areas are usually warmer than their surroundings), flooding from heavy precipitation, and sea level rises in coastal cities.
The monsoon season is projected to have a delayed onset over North and South America and West Africa and a delayed retreat over West Africa, the IPCC report says.
Over South Asia, East Asia and West Africa, increases in monsoon precipitation caused by warming from greenhouse gas emissions were counteracted by decreases in monsoon rains due to cooling from human-caused aerosol emissions over the 20th century, it adds.
Increases in West African monsoon precipitation since the 1980s were partly due to the growing influence of greenhouse gases and reductions in the cooling effect of human-caused aerosol emissions over Europe and North America, the report states.
Heavy precipitation and associated flooding events are projected to become more intense and frequent in the Pacific Islands and across many regions of North America and Europe, the new report says, and such changes may also occur in some regions in Australasia and Central and South America.
Several regions in Africa, South America, and Europe are also projected to experience an increase in frequency and/or severity of agricultural and ecological droughts. Such increases are also projected to occur in Australasia, Central and North America, and the Caribbean.
“With every increment of global warming, changes get larger in regional mean temperature, precipitation, and soil moisture,” the report says.
“Projected changes in extremes are larger in frequency and intensity with every additional increment of global warming.”
There is high confidence in an earlier onset of spring snowmelt, with higher peak flows at the expense of summer flows in snow-dominated regions globally, the report’s authors add.
“A warmer climate will intensify very wet and very dry weather and climate events and seasons, with implications for flooding or drought, but the location and frequency of these events depend on projected changes in regional atmospheric circulation, including monsoons and mid-latitude storm tracks,” they state.
IPCC Working Group 1 co-chair Panmao Zhai said: “Climate change is already affecting every region on Earth, in multiple ways. The changes we experience will increase with additional warming.
“Stabilising 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.”
Working group 1 co-chair Valérie Masson-Delmotte said the report was a reality check. “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,” she said.
Masson-Delmotte said that, with further warming in the coming years, the report’s authors expect to see new extremes that are unprecedented in magnitude and frequency and occur in regions that have never encountered such extremes before.
“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,” Masson-Delmotte said.
“In this report we show that, over the course of this century, global ocean temperature is projected to rise two to eight times as much as it has increased since the early 1970s.”
“The melting of the Greenland and Antarctic ice sheets will continue for thousands of years. This means that the sea level will keep rising … the rate of ice sheet loss has increased by a factor of four in the past thirty years.”
These irreversible changes can be slowed down with rapid, strong, and sustained reductions in emissions and other changes can be stopped if greenhouse gas emissions are deeply reduced, Masson-Delmotte said.
Asked by a journalist about the effect of the Covid-19 pandemic on climate change, Masson-Delmotte said: “Our report shows that, due to the lockdown implemented in the pandemic context, there have been temporary reductions in emissions of CO2, a few percent at the global scale, but these temporary reductions were not sufficient to have a significant impact.” The increase in CO2 concentration in the atmosphere had continued, she said.
There had also been reductions in emissions of air pollutants, Masson-Delmotte said, but these were temporary reductions as well that led to immediate improvements in air quality.
The executive director of the United Nations Environment Programme, Inger Andersen, said: “Nobody’s safe and it’s getting worse faster. We must treat climate change as an immediate threat, just as we must treat the connected crises of nature and biodiversity loss and pollution and waste as immediate threats.
She added: “We understand that climate change exacerbates already grave risks to biodiversity and natural managed habitats. Ecosystem degradation damages nature’s ability to reduce the force of climate change.”
Andersen says every business, every investor, and every citizen needs to play their part. “We can’t undo the mistakes of the past, but this generation of political and business leaders, this generation of conscious citizens, can make things right.
“This generation can make the systemic changes that will stop the planet warming, help everyone adapt to the new conditions, and create a world of peace, prosperity, and equity.”
The new IPCC report includes an interactive atlas.The atlas has two components:
- the regional information component, which provides access to climate change information (variables and derived indices) from the main datasets used in the report, and
- the regional synthesis component, which enables users to explore key synthesised assessments “building on multiple lines of evidence across the Working Group 1 reference regions”.
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