The authors of the new paper found this prehistoric change caused a retreat in the forests that blanketed the Paleocene-Eocene world, causing them to die off as the Earth browned rather than greened, a finding they state has \u201cchilling implications\u201d for today\u2019s world.<\/p>\n
Fragments of fossilized leaves like these helped the authors recreate the forest canopies of 56m years ago. Photograph: Dr. Regan Dunn<\/p>\n
\u201cWhat we see is that as the carbon dioxide ramped up, the forests became very dense but then subsequently collapsed, opening up dramatically,\u201d said Regan Dunn, a researcher at La Brea Tar Pits and the Natural History Museum of Los Angeles County, who led the study.<\/p>\n
\u201cAround 60% of the biomass of the standing vegetation was gone, it was a huge loss. This should be a concern because the rate of carbon release has never been higher than now.\u201d<\/p>\n
Dun added: \u201cForests are some of our best friends and allies but we are already seeing them die back, be cut down and consumed by wildfires. It\u2019s happening quickly, every summer the change seems faster and faster.\u201d<\/p>\n
Plants like trees require carbon to build their structures and, along with water and sunlight, provide food. Once the world started to burn coal, oil and gas in huge volumes from the industrial revolution onwards, the amount of emitted carbon dioxide surged at an unprecedented rate, with atmospheric concentrations of CO2 rising<\/a> by more than 50% in little over a century.<\/p>\n This increase in carbon did initially help boost<\/a> some plant life, a change that has been seized upon by those who question the facts of climate science. Prominent figures in Donald Trump\u2019s administration have argued that burning fossil fuels is good for the environment.<\/p>\n \u201cCO2 was never a pollutant,\u201d Doug Burgum, the interior secretary, told<\/a> Fox Business earlier this year as the federal government moved to erase<\/a> its own power to address the climate crisis. \u201cWhen we breathe, we emit CO2. Plants need CO2 to survive and grow. They thrive with more CO2.\u201d<\/p>\n On the same TV network last year, Chris Wright, Trump\u2019s energy secretary, said<\/a> that there were \u201cpluses\u201d to global heating as well as negatives. \u201cA warmer planet with more CO2 is better for growing plants,\u201d Wright claimed.<\/p>\n The authors compared the cuticle structure of modern leaves (pictured above under epifluorescence microscopy) with fossil leaf cuticles to create a model for canopy cover. Scale bar is 50 microns (0.05 mm). Photograph: Dr. Regan Dunn<\/p>\n Experts have previously rejected<\/a> such claims as false, with the new research paper, published in Science, showing that the Earth\u2019s past experience demonstrates that trees require much more than CO2 to thrive.<\/p>\n Extra carbon dioxide traps more heat, causing trees to struggle amid extreme temperatures and a lack of key nutrients. Hotter conditions can also trigger outbreaks of pests and disease, weakening trees further, and dry out vegetation that then explodes into huge wildfires, such as those that have engulfed<\/a> much of Canada and western Europe this summer.<\/p>\n The switch from greening forests to browning forests occurred around 2000, the new paper states, when the impacts of drought and heat stress overtook the benefits of extra CO2. Since then, evidence has piled<\/a> up<\/a> of escalating global tree mortality, including trees in the tropics dying<\/a> of dehydration.<\/p>\n
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