The Intergovernmental Panel on Climate Change (IPCC) has raised a "climate alarm" with the publication of Climate Change 2021: the Physical Science Basis, which warns that climate change is already affecting every region on Earth, in multiple ways.
This report, which saw hundreds of scientists review more than 1,400 studies to evaluate how human activity is contributing to the Earth's climate change, has called for immediate action to the "immediate threat" of climate change.It found that the main human causes of climate change are the "heat-absorbing greenhouse gases (GHG) released by fossil fuel combustion, deforestation, and agriculture", among others.
Many of the changes observed in the climate are unprecedented in thousands, if not hundreds of thousands of years, the report states. And some of the changes already set in motion - such as continued sea-level rise - are irreversible over hundreds to thousands of years, according to the IPCC.Climate change caused by humans
The report shows that human activity caused the Earth's temperature to increase by 1.1°C between 1850-1900. Averaged over the next 20 years, global temperature is expected to reach, or exceed, 1.5°C of warming.This is an average figure, with some parts of the world, for example, the Arctic, heating faster than others.
With 1.5°C global warming, there will be increasing heat waves, longer warm seasons and shorter cold seasons, according to the report.At 2°C of global warming, heat extremes would more often reach critical tolerance thresholds for agriculture and health, the report shows.
The report also states that levels of CO2 emissions were higher in 2019 than any time in at least two million years. And, that levels of methane and nitrous oxide - second and third-highest contributors of climate change, behind CO2 - were higher in 2019 than at any time in at least 800,000 years.Not just about temperature
But it is not just about temperature, the report has found. Climate change is bringing about multiple different changes in different regions, including 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.
Climate-change reality check
“This report is a reality check,” said IPCC working group co-chair, Valerie 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.”The report also stated that strong and sustained reductions in CO2 emissions and other GHGs would limit climate change. While benefits for air quality would come quickly, it could, however, take 20-30 years to see global temperatures stabilise, according to the IPCC.
