Impacts: How hot could it get?
Image @redcharlie
Does it really matter if it gets this hot?
It’s not just the amount of warming, it’s the speed of change, which is also accerating. 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 modern 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 already disrupting entire ecosystems, bringing pests and diseases into new areas that aren’t adapted to them, driving species to extinction (Fig. 7) and threatening multiple life-supporting ecosystem services that we cannot exist without, which is why climate change is an existential threat.
Heat thresholds for humans have been poorly defined in part because public-health bodies have over-relied on a theoretical study published in 2010… In that paper, researchers used mathematical models to define the ‘wet-bulb temperature’ (WBT) at which a young, healthy person would die after six hours. WBT is a measure that scientists use when studying heat stress because it accounts for the effects of heat and humidity. The models churned out a WBT of 35°C as the limit of human survival. At that threshold, the body’s core temperature would rise uncontrollably. But the model treated the human body as an unclothed object that doesn’t sweat or move, making the result less applicable to the real world… In a 2021 study, Kenney and his colleagues provided a better estimate: a WBT survival limit of around 31°C. They calculated it by tracking the core body temperature of young, healthy people under different combinations of temperature and humidity while they were cycling. – Nature News 14 August 2024
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
What’s the difference between 1.5°C, 2°C, or a bit more?
These temperatures 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. The Arctic is warming much faster than elsewhere, in some areas as much as 3°C warmer across parts of the Greenland ice cap that were once -2°. This means the the temperature is above freezing. You cannot negotiate with the melting point of ice, so vast areas already are melting, 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. By 2022, average temperatures in New Zealand reached 1.5°C (Fig. 5), increasing the frequency of warm extreme from 93% to 234% (Fig. 6). That means even more frequent and more powerful storms, droughts, floods, and marine heatwaves. In the ocean, increased heat and reducing oxygen is already changing entire ecosystems.
Every fraction of a degree counts.
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 7 and 8 are examples. Click on any image to see the full range on Carbon Brief’s website.
