9 Aug 2021
EXPLAINER: WHAT THE NEW IPCC REPORT SAYS ABOUT
EXTREME WEATHER AND CLIMATE CHANGE
12 August 2021
Author
Robert McSweeney
Source(s)
Carbon Brief
The new report from the Intergovernmental Panel on
Climate Change (IPCC) on the science of climate change lands in the aftermath
of a series of deadly extreme weather events around the world.
From the record-breaking “heat dome” in the Pacific
north-west and the wildfires that followed, to the catastrophic flooding in
Europe and China and rainfall-induced landslides in India, extreme weather has
frequently hit the headlines in 2021.
It is fitting, then, that the mammoth document – which
forms the working group one (WG1) section of the IPCC’s sixth assessment report
(AR6) – includes a dedicated chapter on weather extremes for the first time.
The chapter “assesses changes in weather and climate
extremes on regional and global scales, including observed changes and their
attribution, as well as projected changes”, the report says.
Among its key conclusions is that it is an
“established fact” that human-caused greenhouse gas emissions have “led to an
increased frequency and/or intensity of some weather and climate extremes since
pre-industrial times”.
It adds that the latest scientific evidence
strengthens the verdict of the IPCC’s 2018 special report on 1.5C of warming
that “even relatively small incremental increases in global warming (+0.5C)
cause statistically significant changes in extremes on the global scale and for
large regions”.
In this explainer, Carbon Brief draws out what the
reports says on different categories of extremes and how they are – and will be
– influenced by a warming climate.
Framing: It is an “established fact” that
human-caused emissions of greenhouse gases “have led to an increased frequency
and/or intensity of some weather and climate extremes”.
Attribution: How it has “emerged as a growing
field of climate research with an increasing body of literature”.
Heat: It is virtually certain that “there has
been increases in the intensity and duration of heatwaves and in the number of
heatwave days at the global scale”.
Heavy rainfall: The frequency and intensity of
heavy rainfall events “have likely increased at the global scale over a
majority of land regions”.
Flooding: Models project “a larger fraction of
land areas to be affected by an increase in river floods than by a decrease in
river floods”.
Drought: “More regions are affected by increases
in agricultural and ecological droughts with increasing global warming”.
Tropical cyclones: “It is likely that the
proportion of major TC intensities and the frequency of rapid intensification
events have both increased globally over the past 40 years.”
Compound events: “Compound hot and dry conditions
become more probable in nearly all land regions as global mean temperature
increases.”
Summary tables: Two tables provided by the IPCC
that synthesise the observed changes in extremes and contribution by human
influences, and projections under 1.5C, 2C and 4C of warming.
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