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A5C16G Farmer in Bangladesh. Image shot 09/2006. Exact date unknown.
Farmer in Bangladesh, 2006. Credit: Simon Rawles/Alamy Stock Photo.
29 May 2018 21:00

Guest post: Exceeding 1.5C of global warming will hit poorest the hardest

Multiple Authors

Guest postsGuest post: Exceeding 1.5C of global warming will hit poorest the hardest

Dr Andrew King is a climate scientist at the University of Melbourne and Luke Harrington is a climate scientist at the University of Oxford

Climate change is increasing the frequency of heat waves, changing rainfall patterns, raising sea levels and damaging coral reefs through increasing bleaching events.

These effects of climate change are pervasive, so the vast majority of the global population will be impacted in some way as the world warms. However, these impacts will not be felt equally from one country to the next.

Our research, published today in Geophysical Research Letters, shows that it will be the poorest nations who will see the biggest shifts in local climate.

Limiting global warming benefits the tropics

The Paris Agreement aims to keep global warming “well below” 2C above pre-industrial levels with a preferential limit of 1.5C. The Agreement is motivated by the recognition that unchecked global warming will likely have dangerous consequences for the planet.

But keeping to the 1.5C limit will be extremely challenging given the emissions trajectory we are following and the fact that we have had more than 1C of global warming to date.

In our study, we examine the consequences of missing the 1.5C limit in terms of the change people experience in their local climate. We do this using the “signal-to-noise” ratio.

The weather we experience every day is a combination of the long-term trend of climate change – the “signal” – and the short-term fluctuations of natural variability – the “noise”. In areas where temperatures are less variable, a smaller amount of warming is needed before the change in climate becomes perceptible.

So, for example, the warming to date is more noticeable in tropical regions – Singapore, for example – than it is in the mid-latitudes where month-to-month temperature variations are much higher, such as New York or Melbourne.

Society and ecosystems have adapted to the range of historical temperatures experienced in their location, so the signal-to-noise measure of climate change is relevant for everyone.

In general, missing the 1.5C limit and reaching 2C of warming will mean a more palpable change in local temperatures in the tropics than at higher latitudes. You can see this in the map below, which shows higher signal-to-noise near the equator, shown in red, and lower signal-to-noise outside the tropics.

World map of warming.More perceptible warming is projected over the tropics than at higher latitudes

More perceptible warming is projected over the tropics than at higher latitudes. Red shading denote higher signal-to-noise compared with oranges and yellows. Source: Adapted from King & Harrington (2018)

The inequality of climate change

We wanted to investigate how shifts in local climate from 1.5C to 2C of global warming would affect what people actually experience in their own part of the world.

It has previously been shown that global climate change has affected the poorest first, so we investigated whether this effect is projected under future climate change and the sensitivity of this effect to different scenarios of how society develops in future – known as “shared socioeconomic pathways” (SSPs).

We compared the signal-to-noise ratio data with population and gross domestic product (GDP) data, first using 2010 estimates, at every location across the world to investigate the relationship between local climate change and current wealth patterns.

As the less economically developed areas of the world tend to be in the tropics and the more developed economies are in the higher latitudes, we see a strong inverse relationship. This mean, in general, the wealthiest will experience less perceptible climate change than the poorest.

For example, we project that the people of the UK – the first country to industrialise and one of the wealthiest countries – would experience less than half the level of perceptible climate change than the people of the Democratic Republic of Congo, one of the poorest countries in the world.

This result holds true when we look across different SSPs by the middle of this century – by which time 2C may have been breached. Low-income countries are consistently the ones which will experience the largest perceptible shifts in local climate beyond the 1.5C limit. And these countries often have a limited capacity to adapt to a changing climate.

This result is remarkably clear given we are only examining a half-a-degree difference in global temperature.

The graphs below show the relationship between each location’s signal-to-noise and future GDP per capita in 2050. The three scenarios, from a future world where sustainability is given a high priority (left-hand plot), to a more fractured world with a more national focus (right-hand plot), show the poorest places are projected to experience a bigger shift in climate in all cases.

Scatter plot graphs show that Under future potential pathways, the inequality of perceptible climate change remains

Under future potential pathways, the inequality of perceptible climate change remains. Scatter plots between the local signal-to-noise ratio from 1.5C to 2C global warming (x-axis) and GDP per capita under three scenarios for 2050 (y-axis). Source: Adapted from King & Harrington (2018)

An impetus to act

Keeping global warming to low levels, as signatories to the Paris Agreement are aiming to do, has many benefits compared with the alternative of a 3C or 4C warmer world.

Previous work has shown that this would reduce the expected increase in frequency of heat extremes and their impacts in many places around the world – and similarly for droughts and extreme heavy rain events. There would be benefits for many of the world’s plant and animal species, as well as entire ecosystems including the Great Barrier Reef.

Limiting global warming would also help to reduce the barriers to development in the poorest parts of the world. By reducing greenhouse gas emissions more rapidly the developed world would put less of the burden of the impacts of climate change on the developing world.

This should incentivise stronger emissions reductions globally as the drive to eradicate absolute poverty and reduce inequality – among other UN Sustainable Development Goals – depend heavily on limiting global warming.

Unfortunately, the alternative – where greenhouse gas reductions are lethargic – means a warmer world where the poorest regions pay the price of inaction.

King, A. D. and Harrington, L. J. (2018) The Inequality of Climate Change from 1.5C to 2C of Global Warming, Geophysical Research Letters, doi:10.1029/2018GL078430

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