Story highlightsRising CO2 levels are pushing earth beyond any climatic conditions ever experienced by humans, scientists warn.Global mean temperatures are rising much faster than any time since the Pliocene, when sea levels were up to 20 meters higher. CO2 levels are currently 410 parts per million.
(CNN)The last time carbon dioxide levels were this high, Greenland was mostly green, sea levels were up to 20 meters higher and trees grew on Antarctica, according to scientists who warned this week that there is more CO2 in our atmosphere today than in the past three million years.
Using a new computer simulation, researchers at the Potsdam Institute for Climate Impact Research (PIK), in Germany, found that the last time the earth’s atmosphere had a CO2 concentration as high as today’s was during the Pliocene epoch, the geological period 2.6-5.3 million years ago.CO2 emissions from human activities are the leading cause of climate change. Photos: Effects of global warming around the world Photos: Effects of global warming around the worldMelting polar ice caps – The consequences of climate change go far beyond warming temperatures, which scientists say are melting the polar ice caps and raising sea levels. Click through the gallery for a look at 10 other key effects of climate change, some of which may surprise you.Hide Caption 1 of 11 Photos: Effects of global warming around the worldDrought – In the coming decades climate change will unleash megadroughts lasting 10 years or more, according to a new report by scholars at Cornell University, the University of Arizona and the U.S. Geological Survey. We’re seeing hints of this already in many arid parts of the world and even in California, which has been rationing water amid record drought. In this 2012 photo, a man places his hand on parched soil in the Greater Upper Nile region of northeastern South Sudan.Hide Caption 2 of 11 Photos: Effects of global warming around the worldWildfires – There’s not a direct link between climate change and wildfires, exactly. But many scientists believe the increase in wildfires in the Western United States is partly the result of tinder-dry forests parched by warming temperatures. This photo shows a wildfire as it approaches the shore of Bass Lake, California, in mid-September. Hide Caption 3 of 11 Photos: Effects of global warming around the worldCoral reefs – Scientists say the oceans’ temperatures have risen by more than 1 degree Fahrenheit over the last century. It doesn’t sound like much, but it’s been enough to affect the fragile ecosystems of coral reefs, which have been bleaching and dying off in recent decades. This photo shows dead coral off the coast of St. Martin’s Island in Bangladesh.Hide Caption 4 of 11 Photos: Effects of global warming around the worldFood prices – A U.N. panel found in March that climate change — mostly drought — is already affecting the global agricultural supply and will likely drive up food prices. Here, in 2010, workers on combines harvest soybeans in northern Brazil. Global food experts have warned that climate change could double grain prices by 2050. Hide Caption 5 of 11 Photos: Effects of global warming around the worldPollen allergies – Are you sneezing more often these days? Climate change may be to blame for that, too. Recent studies show that rising temperatures and carbon dioxide levels promote the growth of weedy plant species that produce allergenic pollen. The worst place in the United States for spring allergies in 2014, according to the Asthma and Allergy Foundation of America? Louisville, Kentucky. Hide Caption 6 of 11 Photos: Effects of global warming around the worldDeforestation – Climate change has not been kind to the world’s forests. Invasive species such as the bark beetle, which thrive in warmer temperatures, have attacked trees across the North American west, from Mexico to the Yukon. University of Colorado researchers have found that some populations of mountain pine beetles now produce two generations per year, dramatically boosting the bugs’ threat to lodgepole and ponderosa pines. In this 2009 photo, dead spruces of the Yukon’s Alsek River valley attest to the devastation wrought by the beetles.Hide Caption 7 of 11 Photos: Effects of global warming around the worldMountain glaciers – The snows capping majestic Mount Kilimanjaro, Africa’s highest peak, once inspired Ernest Hemingway. Now they’re in danger of melting away altogether. Studies suggest that if the mountain’s snowcap continues to evaporate at its current rate, it could be gone in 15 years. Here, a Kilimanjaro glacier is viewed from Uhuru Peak in December 2010.Hide Caption 8 of 11 Photos: Effects of global warming around the worldEndangered species – Polar bears may be the poster child for climate change’s effect on animals. But scientists say climate change is wreaking havoc on many other species — including birds and reptiles — that are sensitive to fluctuations in temperatures. One, this golden toad of Costa Rica and other Central American countries, has already gone extinct.Hide Caption 9 of 11 Photos: Effects of global warming around the worldAnimal migration – It’s not your imagination: Some animals — mostly birds — are migrating earlier and earlier every year because of warming global temperatures. Scholars from the University of East Anglia found that Icelandic black-tailed godwits have advanced their migration by two weeks over the past two decades. Researchers also have found that many species are migrating to higher elevations as temperatures climb.Hide Caption 10 of 11 Photos: Effects of global warming around the worldExtreme weather – The planet could see as many as 20 more hurricanes and tropical storms each year by the end of the century because of climate change, according to a 2013 study published in the Proceedings of the National Academy of Sciences. This image shows Superstorm Sandy bearing down on the New Jersey coast in 2012.Hide Caption 11 of 11The amount of CO2 in the atmosphere today is “unnatural”, lead-author Matteo Willeit told CNN.Willeit said that according to the simulation CO2 levels should not be higher than 280 parts per million (ppm) without human activity, but that they are currently 410 ppm and rising.Read MoreGlobal mean temperatures are rising much faster than any time since the Pliocene, Willeit added. In that time they have never exceeded pre-industrial levels by more than 2°C, but current models show that temperatures will rise by 4°C between 2000 and 2100 if steps are not taken to slash emissions, he said.Into unknown territoryWilleit said rising CO2 levels are pushing earth beyond any climatic conditions ever experienced by humans.If CO2 levels and temperatures continue to rise, “our planet will change” and sea levels will rise by one or two meters in the next 200 years, he added.'Dead corals don't make babies': Great Barrier Reef losing its ability to recover from bleaching This research isn’t the first to suggest that today’s CO2 levels are the highest since the Pliocene, but the Potsdam researchers say their work is the first to combine ocean-floor sediment data with analysis of past ice volumes, and is more sophisticated than other model studies.Scientists at a Royal Meteorological Society meeting on the climate of the Pliocene in London on Wednesday discussed how sedimentary records and plant fossils from near Antarctica show that during the Pliocene epoch Arctic summer temperatures were 14°C higher than today.Professor Martin Siegert from Imperial College London, speaking at the event, said the findings offered a view of the earth’s future if drastic steps are not taken to address global warming.