New tool tracks global contributions to climate change

University of East Anglia (UEA) researchers in the UK have published findings that show how countries have contributed to global warming through their emissions of key greenhouse gases since 1850.

The work builds on published records of historical emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) – gases that have made significant contributions to warming from the pre-industrial period to 2021. In a critical decade for climate policy, this marks a new effort to track impacts.

A team of researchers led by Dr Matthew Jones of the Tyndall Centre for Climate Change Research calculated the global mean surface temperature response to emissions of all three gases, and national contributions to warming resulting from emissions of each gas, including those from fossil fuel and land use sectors.

The findings provide a “ranking” of countries that have contributed most to global warming, as well as insights into how they have changed in recent decades.

According to the research, the largest contributors to warming up to 2021 through emissions of all three gases since 1850 were, first, the USA, then China, Russia, Brazil, India, Indonesia, Germany, UK, Japan, and Canada. CO2 has contributed the most to warming, the research found.

The new dataset will prove a tool for tracking the effect of changing national emissions on warming, and hopefully see the contributions by all countries level off as commitments to reach net-zero emissions are met or surpassed, says Dr Jones.

“Countries have made commitments to reduce their emissions of CO2, CH4 and N2O with the goal of avoiding the most detrimental impacts of climate change, including from drought, wildfires, flooding and sea level rise,” he says.

“Notably, the combined contributions to warming from Brazil, South Africa, India and China rose from 17 per cent in 1992 to 23 per cent in 2021, whereas the contribution from the industrialised OECD countries fell slightly from 47 per cent to 40 per cent.

“[This illustrates] how the contributions to global warming from industrialising nations are rising as their emissions grow relative to early industrialisers, many of which have begun to decarbonise.”

The research also highlights how national contributions can vary across countries at different stages of industrialisation. In half of the world’s countries, the land use and forestry sectors still make a dominant contribution to the warming when considering all emissions since 1850.

Because of their long-lived or powerful effects on climate, the emissions of CO2, CH4 and N2O are regulated by the United Nations Framework Convention on Climate Change (UNFCC), with targets set for CO2 through nationally determined contributions (NDCs) under the Paris Agreement. Around 90 per cent of NDCs include targets for CH4 and N2O. Therefore, keeping track of the emissions of CO2, CH4 and N2O and the climatic responses is especially important for ensuring accountability with respect to NDCs.

The findings also seek to inform the first Global Stocktake of the UNFCCC, the process set out in the Paris Agreement to assess national progress towards achieving the pact’s goal to limit global warming to 1.5°C. The findings will be presented at COP28 this year.

The UEA says that, unlike previous datasets of national contributions, this work will be updated regularly as new national emissions figures become available, for example alongside publication of the Global Carbon Budget.

“This dataset is uniquely positioned to inform climate policy and benchmarking,” says Dr Jones. “It should become a living resource for continually tracking contributions to climate change and, more importantly, how those are changing.”

The research is published in Scientific Data journal.

Image by Tima Miroshnichenko.

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