By all accounts, the climate crisis is already here. Deadly heat domes across the Pacific Northwest, a petroleum pipeline leak in the middle of the ocean that set the Gulf of Mexico on fire, and the deadly floods in Germany and Belgium in the past few weeks alone have proved that the world is changing in response to how we have changed it.*
No one should be surprised by this. For decades, scientists have been ringing the alarm bell about anthropogenic climate change. Over 30 years ago, NASA scientist James Hansen told the U.S. Congress that the “greenhouse effect is here.” And long before then, in the 1800s, scientists like Svante Arrhenius calculated that doubling the amount of CO2 that was in the atmosphere in 1895 would lead to global warming of 5 to 6 degrees Celsius in average global temperatures. “That wasn’t too far off,” said Peter Kalmus, a climate scientist at NASA’s Jet Propulsion Laboratory, speaking on his own behalf. It was just that Arrhenius’s timeframe for how quickly humans would emit those gasses was way off, Kalmus added: “It only took about 125 years for that increase in CO2 fraction that he thought would take 3000 years. He grossly underestimated the rate of emissions from burning fossil fuels that we actually did.”
Arrhenius’s original prediction represents a lot of the current problems faced by climate change models. Understanding where we are on the climate change timeline requires multiple steps—we need to know how much greenhouse gas has been emitted, how much those greenhouse gases have increased the global temperature, and then finally, we need to take one last step that even Arrhenius never took—we need to understand how those changes in global temperature will affect the climate we experience. It’s this last bit that is trickiest—we know the current proportion of carbon in our atmosphere (currently around 420 parts per million), what we don’t know is how to accurately predict all the consequences of the temperature increase caused by that extra carbon.