Experts warn that due to a strengthening sun, the same carbon concentrations will cause more warming in future than in previous periods of high carbon dioxide
The earth’s climate may be heading towards warmth not seen in the past half a billion years due to carbon dioxide concentrations heading towards values not seen in the past 200 million years as well as the sun getting stronger over time.
Looking at the past to understand the future:
Most changes that occur on Earth happen on very long timescales of millions of years or more. However, over the past 150 years global temperatures have increased by around 1°C, ice caps and glaciers have shrunk, polar sea ice has melted which caused the rise of sea levels.
Despite Earth’s climate undergoing similar changes before, but the current speed of change is highly unusual, according to scientists studying the matter. They have concluded that carbon dioxide hasn’t been added to the atmosphere as rapidly as today for at least the past 66 million years.
According to new study published in Nature Communications, if humans continue on the current path and exploit all convention fossil fuels, and the rate of CO₂ emissions continues rising, the absolute climate warming is also likely to be unprecedented in at least the past 420m years.
50 million years ago, global average temperatures were 10-15°C warmer than today, Earth was in what is called a “greenhouse” climate state. The Polar Regions were ice-free, palm trees grew on the coast of Antarctica, and alligators and turtles wallowed in swamp-forests in what is now the frozen Canadian Arctic.
In fact, despite the current warming, Earth is still technically in an “icehouse” climate state meaning there is ice on both poles. Our planet has cycled naturally between the two climate states every 300m years or so.
Before the industrial revolution, CO₂ concentrations were 280 parts per million, or ppm, meaning that for every million molecules in the atmosphere, about 280 of them were CO₂ molecules.
Today, due to burning of fossil fuels, CO₂ concentrations are 400 ppm. And if we keep up with the current rates, by the year 2250, the CO₂ concentrations will be around 2,000ppm
Earth has experienced similar concentrations several times in the past. 200 million years ago, when dinosaurs first evolved, Earth had a greenhouse climate state with atmospheric CO₂ around 2,000-3,000ppm. The dinosaurs thrived in this weather.
However, that doesn’t mean humans will. Major socio-economic challenges will occur due to the rise of CO₂ concentrations to 2,000 or more ppm. Also, new studies show that the same carbon concentrations will cause more warming in future than in previous periods of high carbon dioxide due to the sun’s increased brightness.
The combined effect of the sun’s changing strength and the varying greenhouse effect is what’s alarming. Throughout the Earth’s history, as the sun became stronger through time, atmospheric CO₂ gradually decreased. On average, both changes cancelled each other out.
Scientists haven’t been able to find similar conditions to the ones that are currently shaping up in the Earth’s 420m years, making the future a great unknown.