The relationship between Earth’s surface temperature and concentrations of carbon dioxide (CO₂), the main greenhouse gas, in the planet’s atmosphere has been at the basis of climate change science for decades. But a new study published this Thursday in the prestigious magazine Science which reconstructs the evolution of the planet’s temperatures in the current eon (a time period spanning the past 540 million years) further strengthens that link, because it places CO₂ as the “dominant factor controlling global climate variations throughout the Phanerozoic,” as the current eon is called.
Researchers have reconstructed the evolution of temperatures over the past 485 million years and have found a clear correlation. The link is so consistent and sustained over the millions of years analysed that the authors themselves describe it as “surprising” in the article published on Thursday. Because throughout this immense period of time, which includes glaciations and much warmer periods than the present, the authors expected to locate other dominant factors and drivers of climate change not related to carbon dioxide, such as variations in the luminosity of the sun or other greenhouse gases. In any case, the authors admit that the nature of this link is probably “complex” and will require further research.
The authors of the research combined indirect geological data from ice, marine sediments and tree rings with simulations of models of the Earth system to trace the evolution of temperatures in this study since the appearance of non-microscopic life on the planet.
The other major finding of this study, led by Emily J. Judd, a researcher at the Smithsonian National Museum of Natural Historyis the wide variation in temperatures that has occurred over the period of time evaluated, with differences of up to 25 degrees Celsius. In those 485 million years, the range of average temperatures goes from 11 degrees in the late Pleistocene (between 129,000 and 11,000 years ago) to 36 degrees in the Turonian (about 90 million years ago). This is a much greater oscillation than that identified so far in previous paleoclimatic studies. In addition, most of the Earth’s history has taken place in warmer rather than colder climates, the study adds.
The average temperature of the planet is currently around 16 degrees Celsius, which would be at the lower end of the range for the current eon. However, the planet is undergoing a climate change that is causing rapid global warming. The difference with previous climate changes over the last 500 million years is that this time the increase in CO₂ concentrations in the air is motivated by human action, as has already been made clear by the IPCC, the international panel of experts that lays the scientific foundations for global warming. The main reason is the massive use of fossil fuels (coal, oil and gas), which when burned to produce energy release carbon dioxide that ends up largely in the atmosphere.
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The greater the presence of CO₂ in the air, the more heat is stored on the planet’s surface, which leads to higher temperatures. This is the basis of the greenhouse effect that is behind global warming. But another of the major differences with the climate changes experienced on the planet is the speed at which this concentration of carbon dioxide is increasing now. Only seven decades have passed since humans began to burn fossil fuels on a massive scale, which has led to a drastic increase in the accumulation of this gas in the air.
We have to go back about two million years (before the appearance of humans) to find a similar concentration of this gas in the Earth’s atmosphere as there is today, according to the latest major IPCC review. And we have to go back thousands of years to find an average temperature of the Earth’s surface as high as it is now. As long as humans continue to emit greenhouse gases, the temperature increase that has accelerated in recent decades will not be stopped.
Current climate change can be measured on a scale of centuries and millennia, while the study published on Thursday paints a portrait of 500 million years (the period of time in which macroscopic organisms have developed on Earth: plants, fungi, animals and algae). According to its authors, knowing the evolution of the Earth’s climate in such a broad way can help predict how its future development will be in a context of climate change such as the current one.
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