Saturday, March 02, 2024

Characterizing climate change from heating, not merely temperature


Climate change goals

Peer-Reviewed Publication

WORLD SCIENTIFIC

Characterizing Climate Change from Heating, not merely Temperature 

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CREDIT: WORLD SCIENTIFIC



Current human–induced climate change arises primarily from the heating of the planet from changes in atmospheric composition. Only one manifestation of this is temperature change.  Yet the focus of many media reports is on temperatures and whether the Paris Agreement targets of 1.5°C or 2°C have been breached or threatened. A new paper published in the Journal of Climate Action, Research, and Policy challenges this framing.

The increasing amount of greenhouse gases (notably carbon dioxide from burning fossil fuels) in the atmosphere leads to Earth’s Energy Imbalance (EEI) and altered flows of energy through the climate system. The dissemination of excess energy is partly what determines how climate change is manifested. Some of the extremes being experienced — especially those involving drought, convection, storms, flooding, and the water cycle — are mostly driven by aspects of heating. While temperature contributes through the water–holding capacity of the atmosphere, it is more a consequence than a cause. After all, water is the air–conditioner of the planet.  Natural climate variability — such as the strong El Niño currently underway — generally determines where new extremes occur and can lead to confusion as to what is going on. Human–caused change exacerbates the weather and natural variability.

The United Nations — and especially the Intergovernmental Panel on Climate Change (IPCC) in their Summary for Policy Makers — focus on global temperature targets rather than broader facets of climate change including EEI, and do not always adequately discriminate between temperature and heating. This also has consequences for future climate control if or when heating is brought under control by cutting emissions. Improvements are needed in expressing how the climate is changing by properly accounting for the flow of energy through the climate system.

The new climate norm has a warmer ocean and less ice, and some changes on the warmer land mean less and maybe destabilized permafrost. Rainfall character changes substantially. Many changes do not relate directly to global temperature but are nonetheless physically related to the heating climate.

The new paper is authored by Kevin Trenberth, who has watched as climate change (global warming) was ignored, then dismissed, under–reported, largely missing in many disaster reports where it should have been included, to now being blamed for almost everything.

He emphasizes that increased heating often leads to more evaporation from the ocean and terrestrial surfaces. The resulting increased amount of atmospheric water vapor causes more intense storms and heavier rains, raising the risk of flooding.

About the author:

Dr. Kevin E. Trenberth is a Distinguished Scholar at the National Center for Atmospheric Research and an honorary affiliate faculty at the University of Auckland in New Zealand. He has been involved in climate and climate change research throughout his career. He has been prominent in most of the Intergovernmental Panel on Climate Change (IPCC) scientific assessments of Climate Change, including in the inter–governmental meetings that approved the second, third and fourth assessments, and has also extensively served the World Climate Research Programme (WCRP) in numerous ways.

The author is affiliated with the NSF National Center for Atmospheric Research, in Boulder, CO, and the University of Auckland, New Zealand.

Kevin Trenberth: +64 27 771 4868, trenbert@ucar.edu

The paper Characterizing Climate Change from Heating, not merely Temperature can be found in the Journal of Climate Action, Research, and Policy

Climate change disrupts seasonal flow of rivers


Climate change is disrupting the seasonal flow of rivers in the far northern latitudes of America, Russia and Europe and is posing a threat to water security and ecosystems, according to research published today.

Peer-Reviewed Publication

UNIVERSITY OF LEEDS



Climate change is disrupting the seasonal flow of rivers in the far northern latitudes of America, Russia and Europe and is posing a threat to water security and ecosystems, according to research published today.

A team of scientists led by the University of Leeds analysed historical data from river gauging stations across the globe and found that 21% of them showed significant alterations in the seasonal rise and fall in water levels.

The study used data-based reconstructions and state-of-the-art simulations to show that river flow is now far less likely to vary with the seasons in latitudes above 50°N than previously, and that this could be directly linked to changes to the climate caused by human activity.

Until now, evidence suggesting that climate change has had an impact on river flow seasonality has been limited to local studies or has failed to consider the impact of climate change brought about by humans explicitly.

In this study the team used monthly average river flow measurements from 10,120 gauging stations from 1965 to 2014.

For the first time ever, they were able to exclude direct human interventions such as reservoir management or water extraction, to show that widespread reduction in river flow seasonality was driven by climate change.

The results of the research, which was funded by the University of Leeds and the Southern University of Science and Technology in China are published today (29 February) in the journal Science.

Lead author, Hong Wang, a PhD researcher at the University of Leeds and the Southern University of Science and Technology in China, said: “Our research shows that rising air temperatures are fundamentally altering the natural patterns of river flow.

“The concerning aspect of this change is the observed weakening of river flow seasonality, and that this is as a direct consequence of historical human-induced emissions. This signals a sustained and considerable diminishment of river flow seasonality if air temperatures continue to rise.”

Human impact on river flow

Human activities are altering river flow patterns worldwide, both directly through flow regulations such as reservoirs, and indirectly through land use change and the impacts of climate change on air temperature, precipitation, soil moisture, and snowmelt.

Over two-thirds of the world’s rivers have already been altered by humans even without considering the indirect impacts of increases in greenhouse gases and aerosols.

River flow seasonality plays a critical role in the predicted cycle of floods and droughts. A weakening of these peaks and troughs can threaten water security and freshwater biodiversity. For example, a substantial portion of the early meltwater from snowpack depletion may quickly flow into oceans and therefore not be available for human use.

Weakening river flow seasonality - for example due to a reduction in spring and early summer river levels in snowmelt regions - can also have an impact downstream on riverbank vegetation and organisms living in the river itself.

 

Gauging the seasonal flow

In northern North America, the researchers found that 40% of the 119 stations observed showed a significant decrease in river flow seasonality. Similar results were also observed in sSouthern Siberia with 32% of stations showing a significant decrease.

There was a comparable pattern in Europe, with 19% of the river gauging stations experiencing a significant decrease - mainly in northern Europe, western Russia and the European Alps.

In addition, regions in the contiguous United States (the lower 48 states in North America, including the District of Columbia) showed predominantly decreasing trends of river flow seasonality overall, except for rivers in the Rocky Mountains and Florida.

In central North America, the research showed significant decreasing river flow seasonality trends in 18% of the stations.

By contrast, the researchers found a significant increase in river flow seasonality in 25% of the gauging stations in southeast Brazil, showing that changes to the water cycle are having a different impact in some parts of the world.

Dr Megan Klaar, an Associate Professor in the University of Leeds School of Geography and a member of water@leeds, co-authored the research. She said: “The highs and lows of river flow during the different seasons provide vital cues for the species living in the water.

“For example, a lot of fish use particular increases in the water as a cue to run to their breeding areas upstream or towards the sea. If they don’t have those cues, they won’t be able to spawn.”

The research concludes that there is a need to accelerate climate adaptation efforts to safeguard freshwater ecosystems by managing flows to try to recreate some of the natural systems and processes that are being lost.

Professor Joseph Holden, the Director of water@leeds and who supervised Hong Wang’s research, added: “A lot of concern is based upon what climate change will do in the future but our research signals that it’s happening now and that increases in air temperature are driving huge changes in river flow.

“We should be very concerned about what the future holds given accelerating climate change and begin to think about mitigation strategies and adaptation planning to alleviate the future weakening of seasonal river flow, particularly in locations such as western Russia, Scandinavia, and Canada.”

Ends

Notes to editors

Anthropogenic climate change has influenced global river flow seasonality is published today (29 February) in the journal Science

The DOI is 10.1126/science.adi9501

Pictures and illustrations available here

Photo of alpine river in Zinal, Switzerland: Please credit Yoal Desurmont

Illustration 1: Credit Myriam Wares

Email: contact@myriamwares.com

The rapid rise in air temperature, driven by human-induced emissions, is diminishing the seasonal variations in river flow. This weakening pattern of river flow seasonality has the potential to impact riparian vegetation, the life cycles of freshwater biota, and water security.

Illustration 2: Credit Elena Galofaro Bansh

Email: elena@elenabanshart.com

The rapid rise in air temperature, driven by human-induced emissions, is diminishing the seasonal variations in river flow. The homogenized monthly distribution of river flow throughout the year has the potential to impact freshwater ecosystems and water security.

 

For media enquiries or interview requestsplease contact Kersti Mitchell via k.mitchell@leeds.ac.uk

Other institutions involved in the research were:

School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen, China

North China University of Water Resources and Electric Power, Zhengzhou, China

Henan Provincial Key Lab of Hydrosphere and Watershed Water Security, North China

University of Water Resources and Electric Power, Zhengzhou, China

Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland

 

University of Leeds

The University of Leeds is one of the largest higher education institutions in the UK, with more than 39,000 students from more than 137 different countries. We are renowned globally for the quality of our teaching and research.

We are a values-driven university, and we harness our expertise in research and education to help shape a better future for humanity, working through collaboration to tackle inequalities, achieve societal impact and drive change. 

The University is a member of the Russell Group of research-intensive universities, and is a major partner in the Alan Turing, Rosalind Franklin and Royce Institutes www.leeds.ac.uk 

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