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Can climate change be said to cause extreme weather events?

Avon Energy Partner’s Sustainability Analyst, Ben Wrighton, is currently completing his Master’s in Climate Change alongside working for us. Given the recent heat waves experienced throughout Europe, we’re delighted for Ben to share some of his findings in the research linking climate change and extreme weather.


As our planet's climate warms, changes in weather extremes are becoming ever more prevalent and destructive. The IPCC reported it is an “established fact” that the increased frequency and intensity of some extremes can be attributed to an increase in greenhouse gas emissions associated with anthropogenic activities.


But what are weather extremes and how can we attribute climate change to extreme weather events?


Extreme events

An extreme weather event is a rare event due it’s particular location and timing throughout the year. Extreme events can be extremes in temperature and precipitation, floods, droughts, storms as well as a combination (compound event) of events.


But what impact do human activities have and how do we attribute climate change to the increases in extreme weather events?


Anthropogenic emissions and climate change

Human activities such as power generation and urbanisation emit greenhouse gases. Greenhouse gases absorb incoming solar radiation from the sun and allow for the naturally occurring greenhouse gas effect.

However, since 1750, the increased output of greenhouse gases has enhanced the greenhouse gas effect, thus trapping more solar radiation. With an increase in solar radiation, and therefore, an increase in total energy in the atmosphere, the climate system has warmed. To add, warmer air can hold more water vapour in the atmosphere, and so we experience higher frequencies and intensities of intense rains and storms.


Climate Change Attribution

Research over the last 20 year has focused on the question of whether climate change can be said to cause the increased frequency and intensity of extreme weather.


Among researchers there is now an high level of confidence that the rise in global MEAN temperature was caused by anthropogenic activities. It is not completely self-evident that warmer air in the atmosphere, means more extreme temperatures


Although, by definition extreme events are statistically far from the mean (as seen in the schematic below), more recent studies are looking at how climate change has changed the frequency, likelihood and intensity of the extremes.



The frequency is defined as a rate of exceedance of a fixed threshold defined with a historical baseline. Conversely, the severity is defined as a magnitude associated with a given probability. In the majority of extreme weather events, both frequency and severity have been observed to increase, worsening the human impacts.


However, it is less obvious to determine whether the climate extreme was human induced. So researchers attempt to attribute anthropogenic climate change to extreme events by using some combination of: real-world observations, climate-model simulations and statistical techniques with the aim to separate and compare the anthropogenic influence on the climate system from a counterfactual – a climate without human influence.


Observations

The IPCC’s latest report, over 400 extreme weather events studied since 2011, 384 identified human activities as the cause of them.


However, it is important to note that there is natural variability within the climate. This means temperatures may not get higher every year and there will be natural ups and downs. In addition, there will also be spatial variation (variations between locations) and temporal variation (variations in timing and duration) of climate extremes, particularly in rainfall.


This research will be especially important in the future when considering the impact climate change will have on incident insurance and also incentives to reduce national to corporate level emissions


One thing is for sure though…the planet’s temperature is rising, and the frequency and severity of the associated impacts are rising too.



Sources

Chen, A.S., Djordjević, S., Leandro, J. and Savić, D.A., 2010. An analysis of the combined consequences of pluvial and fluvial flooding.

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change

Pidcock, R and McSweeney, R (2021), 'Mapped: How Climate Change affects Extreme Weather around the world.' Carbon Brief.

Swain, D.L., Singh, D., Touma, D. and Diffenbaugh, N.S., 2020. Attributing extreme events to climate change: a new frontier in a warming world.

Yano, J.I. and Manzato, A., 2021. Does More Moisture in the Atmosphere Lead to More Intense Rains?. Journal of the Atmospheric Sciences.







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