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Impacts: How hot could it get?

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How hot could it get?

Summary

If our experiment was to see if we could recreate the Pliocene, we’re doing a really good job! We’re spot-on with that. And for our planet to create a Cretaceous, if we keep going for another 50 years, we’re fine!” – Prof. Martin Seigert, Grantham Institute (Video 2).

  • The Cretaceous, 145 to 65 million years ago, was one of the warmest periods on the planet. Atmospheric CO2 was around 1,000ppm, the average ocean temperature 35°C, there was no ice, anywhere, and temperatures at the poles were 14°C in winter (today, winter temperatures are around -49°C) (See: how we know about past climates).

Does it really matter if it gets this warm?

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. Most plants and animals alive today—including humans, which have only been around for 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 referred to as an ‘existential threat’.

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

Summary

If our experiment was to see if we could recreate the Pliocene, we’re doing a really good job! We’re spot-on with that. And for our planet to create a Cretaceous, if we keep going for another 50 years, we’re fine!” – Prof. Martin Seigert, Grantham Institute (Video 2).

  • The Cretaceous, 145 to 65 million years ago, was one of the warmest periods on the planet. Atmospheric CO2 was around 1,000ppm, the average ocean temperature 35°C, there was no ice, anywhere, and temperatures at the poles were 14°C in winter (today, winter temperatures are around -49°C) (See: how we know about past climates).

Does it really matter if it gets this warm?

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. Most plants and animals alive today—including humans, which have only been around for 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 referred to as 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: On the Brink – UN Emissions Gap Report 2020
Video 2: The Pliocene: The Last Time Earth had over 400 ppm of Atmospheric CO2′; 3.5 hour recording of lectures: The Grantham Institute and Royal Meteorological Society National Meeting, April 2019.

What’s the difference between 1.5°C, 2°C  or a bit more? It’s just half a degree, right?

The temperatures in Figure 2 are global averages, not maximum temperatures. At the poles, average temperatures are up to 5 times this much. Just half a degree hotter is enough to trigger a cascade of dangerous tipping points, over which we have no control and cannot undo.

Think of it this way. If you add half a degree, -0.5°C of warming to ice caps and glaciers that are currently averaging -0.25°C, that would mean they are at +0.25°. That’s enough to melt across vast areas, adding to sea levels rise. Half a degree also changes the way many plants and animals behave, which brings big problems for biodiversity and agriculture, and the spread of diseases. Just a half a degree of warming increases the frequency of warm extremes over New Zealand from 93% to 234% (Fig. 3). That means even more frequent and more powerful storms, droughts, floods, and marine heatwaves.

Every fraction of a degree counts.

Fig. 2: 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 3 and 4 are examples. Click on any image to see the full range on Carbon Brief’s website.

Fig. 3: 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 more than triples the loss of biodiversity in some areas (Image: Carbon Brief).

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