Humans on the verge of causing Earth’s fastest climate change in 50m years
Humans are changing Earths climate at an alarmingly fast rate A new study published in Nature Communications looks at changes in solar activity and carbon dioxide levels over the past 420 million years. The authors found that on our current path, by mid-century humans will be causing the fastest climate change in approximately 50 million years, and if we burn all available fossil fuels, well cause the fastest change in the entire 420 million year record. The study relates to a scientific conundrum known as the faint young sun paradox that early in Earths history, solar output was 30% less intense than it is today, and yet the planet was warm enough to have a liquid ocean. A stronger greenhouse effect due to higher carbon dioxide levels in the atmosphere may be one explanation. Over time, solar output has grown stronger, and atmospheric carbon dioxide levels have fallen due to an effect known as weathering of rocks and an increase in plant life. The authors of this study found that over the past 420 million years, the slow heating of the sun and slow decline of the greenhouse effect have roughly offset each other, leading to a fairly stable long-term global climate. In particular, as shown in the first chart above, Earths climate has been fairly stable over the past several million years. The wiggles in the blue line represent transitions in and out of ice ages, due to wobbles in the Earths orbit around the sun, amplified by changes in the amount of carbon dioxide in the atmosphere (these are known as Milankovich cycles ). The bottom frame in the chart shows the change in forcing (global energy imbalance) caused by the combination of changes in solar activity and the greenhouse effect. When the line is flat, the Earths energy balance is stable, and thus so is its climate. When theres a steep change, something is upsetting that balance and causing a rapid climate change. The five colored lines toward the end of the chart show potential pathways well follow, depending on how much fossil fuels humans burn over the coming decades. In every case the line is already quite steep due to the hundreds of billions of tons of carbon pollution humans have dumped into the atmosphere thus far. The size of the global energy imbalance weve caused is already on par with those previous blue wiggles Earths ice age transitions. If we keep burning lots of fossil fuels, we could soon cause higher carbon dioxide levels and faster climate change than the Earth has seen in 50 million years. If we burn all available fossil fuel reserves (the black Wink12k line), well see faster climate change than in the entire 420 million year record. Its an alarming proposition. Climate deniers will often argue against taking action to curb carbon pollution because climate changed naturally in the past and carbon dioxide levels were higher in the past . One Republican congressman repeated these talking points in the latest House Science committee hearing . While both arguments are technically true, they miss several important points. First, the rate at which were currently causing climate change is alarmingly fast much faster than in most natural climate change events . Second, similar past rapid climate changes have caused mass extinction events . Third, the suns cooler past helped keep temperatures lower. As renowned climate scientist Wallace Broecker once said, The climate system is an angry beast, and we are poking at it with sticks. As this new study shows, our poking sticks are getting bigger and bigger, and were poking the beast faster and faster. Meanwhile, climate deniers are egging us on because the beast has been angered in the past, and were not sure just how soon it will decide to maul us.