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Impacts: How hot could it get?

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How hot could it get?

Summary

  • Today, the amount of carbon dioxide (CO2) in the atmosphere is over 416ppm, temperatures are 1.1°C higher than the pre-industrial era. Following COP27, it is clear that countries will not meet their Paris climate agreement pledges to reduce emissions and keep temperatures under 1.5°C; we are currently on the SSP5-8.5 track for warming of up to 4.4°C by the end of the century (Fig. 1).
Fig. 2: Global surface temperature change; image IPCC 6th Assessment Report
Fig. 1: Projected temperature changes (Image: IPCC AR6 WG1)

CO2 temperatures sea levels past 56 million years

 Fig. 2 The relationships between temperature, CO2, and sea levels over the past 56 million years (Image: IPCC AR6 WG1)

  Impacts

Other sections

Home > Climate wiki > Impacts > How hot could it get?

Summary

  • Today, the amount of carbon dioxide (CO2) in the atmosphere is over 416ppm, temperatures are 1.1°C higher than the pre-industrial era. Following COP27, it is clear that countries will not meet their Paris climate agreement pledges to reduce emissions and keep temperatures under 1.5°C; we are currently on the SSP5-8.5 track for warming of up to 4.4°C by the end of the century (Fig. 1).
Fig. 2: Global surface temperature change; image IPCC 6th Assessment Report
Fig. 1: Projected temperature (Image: IPCC AR6 WG1)

CO2 temperatures sea levels past 56 million years

 Fig. 2 The relationships between temperature, CO2, and sea levels over 56 million years (Image: IPCC AR6 WG1)

Does it really matter if it gets this hot?

It’s not just the amount of warming, it’s the speed of change. The planet hasn’t warmed this fast since the comet wiped out the dinosaurs at the end of the Cretaceous, 65 million years ago. Most plants and animals alive today—including humans, which have been around for only about 200,000 years—evolved to live in an atmosphere where the quantity of greenhouse gases keep in enough heat, but not too much. Adding so much more heat in just a few hundred years has changed the climate too rapidly for many plants and animals to adapt. This is disrupting entire ecosystems, bringing pests and diseases into new areas that aren’t adapted to them, driving species to extinction (Fig. 4) and threatening multiple life-supporting ecosystem services that we cannot exist without, which is why climate change is an existential threat.

“Ecosystems, species, wild populations, local varieties and breeds of domesticated plants and animals are shrinking, deteriorating or vanishing. The essential, interconnected web of life on Earth is getting smaller and increasingly frayed. This loss is a direct result of human activity and constitutes a direct threat to human well-being in all regions of the world.” – Prof. Settele, Global Assessment Report on Biodiversity and Ecosystem Services

“More frequent and intense extreme events, superimposed on long-term climate trends, have pushed sensitive species and ecosystems towards tipping points, beyond ecological and evolutionary capacity to adapt, causing abrupt and possibly irreversible changes”. – IPCC; Climate Change 2022: Impacts, Adaptation and Vulnerability

Video 1: UN Emissions Gap Report 2022
Video 2: The Pliocene –  The Last Time Earth had over 400 ppm of Atmospheric CO2; 3.5 hour recording of lectures from The Grantham Institute and Royal Meteorological Society National Meeting 2019.

What’s the difference between 1.5°C, 2°C  or a bit more?

The temperatures in Figure 1 are global averages, not maximum temperatures. At the poles, due to feedback effects, average temperatures are up to 4 times higher. This is already triggering cascade of dangerous tipping points, over which we have no control, which affects us here in Aotearoa, and which we cannot undo.

Think of it this way. Add 4°C to parts of the Greenland ice cap that were once -3°C. That’s now melting vast areas, adding to sea levels rise. Elsewhere in the world, just 0.5°C changes the way many plants and animals behave, which brings big problems for biodiversity and agriculture, and the spread of diseases. Adding just  0.5°C of warming increases the frequency of warm extremes over New Zealand from 93% to 234% (Fig. 4). That means even more frequent and more powerful storms, droughts, floods, and marine heatwaves.

Every fraction of a degree counts.

Fig. 3: Projected extremes for a rise of 1.5°C (left) and 2°C (right). (Image: NASA)
Fig. 3: Projected extremes for a rise of 1.5°C (left) and 2°C (right). (Image: NASA)

Carbon Brief has extracted data from around 70 peer-reviewed climate studies to show how global warming is projected to affect the world and its regions, based on 1.5°C, 2°C, and even higher warming (based on our current emissions pathway). Figures 4 and 5 are examples. Click on any image to see the full range on Carbon Brief’s website.

Fig. 4: Just a half a degree of warming increases the frequency of warm extremes over New Zealand from 93% to 234% (Image: Carbon Brief).
Fig. 4: Just a half a degree of warming increases the frequency of warm extremes over New Zealand from 93% to 234% (Image: Carbon Brief).
Fig. 5: Just a half a degree of warming more than triples the loss of biodiversity in some areas (Image: Carbon Brief).
Fig. 5: Just a half a degree of warming more than triples the loss of biodiversity in some areas (Image: Carbon Brief).

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