The UN has opened two weeks of diplomatic negotiations between nearly 200 countries to both try to slow global warming and to adapt to the damage already caused by climate change. LSA Associate Dean for Natural Sciences Chris Poulsen investigates climate change throughout Earth’s history by using climate models and observation. He agreed to field some questions about where we are right now. 

LSA: What do you think are the most important findings in the UN’s Intergovernmental Panel on Climate (IPCC) Sixth Assessment Report that came out this past summer?

Chris Poulsen: The most important message of AR6—the IPCC’s sixth assessment report—is that human-induced warming is unequivocal. The previous five reports left some slivers of doubt. This report not only dispensed with those doubts but also stated that climate change is affecting every inhabited region on the globe. Not only is human-induced warming certain, but its impact is global. AR6 also raises the estimate of climate sensitivity—the amount of warming caused by an increase in carbon dioxide.

LSA: The report focuses a lot on the need to reduce carbon emissions in order to slow rising temperatures. Why will global temperatures continue to increase, even if we completely stop emitting carbon right now?

CP: Some studies have suggested that increased warming is “baked in” even after carbon emissions go to zero. This is because some parts of the climate system, including ocean and land ice, respond more slowly to global climate change. It will take them decades to “catch up” to the warming that has already been committed. For example, the Greenland and West Antarctic ice sheets will continue to melt in a warmer world even as emissions reach zero. These studies assume that the CO2 level in the atmosphere remains constant. However, other studies show that once emissions go to zero, the atmospheric CO2 level will start to fall as the ocean and land surface continue to sequester CO2 from the atmosphere. In these studies, the global temperature begins to decrease slightly shortly after emissions reach zero.

At some level, the question about whether the climate will continue to warm slightly or not after we stop emitting carbon is hypothetical—we’re a long way from getting emissions to zero!

LSA: According to the report, even if we do everything right and start reducing emissions now, we will still surpass the critical threshold of 1.5 °C warming by 2030. Limiting the global temperature increase to 1.5–2 °C was the goal of the Paris climate agreement. Are we now looking at a different range of scenarios? 

CP: Current national climate pledges are not adequate to hold warming to 1.5 C. The IEA World Energy Outlook 2021 (WEO21) reports that, even if all pledges are met, CO2 emissions will only decrease by 40 percent by 2050, and the global average temperature will rise to about 2.1 C by 2100. This falls well short of the requirement of net zero emissions by 2050 to stabilize warming at 1.5 C.

Though it’s closing, the door is not yet shut on a 1.5 C future. Limiting warming to that level requires all countries to do more—immediately—to reduce emissions. The WEO21 report outlines four measures that could get us there: a push for electrification that involves massive deployment of renewable energy sources; a rapid reduction in methane emissions from fossil fuel operations; a decrease in energy intensity through a focus on energy efficiency; and an investment in future clean energy technologies.

The COP26 UN Climate Change Conference will take place during the first part of November. That international meeting and any new national commitments that come out of it will very likely determine whether there is still a chance to limit warming to 1.5 C.

LSA: Are scientists able to accurately predict the regional effects of a warming climate? Do we know what Michigan would look like in a world that is 1.5 C warmer?

CP: Predictions of future climate are made using complex physical models of the climate system. These models are incredible tools and are arguably among the most important pieces of software created in the last half century. They are the foundation for much of our knowledge about climate and human-caused climate change, and are used to understand climate impacts and mitigation. One of the pioneers of climate modeling, Syukuro Manabe, was just recently awarded the Nobel Prize in Physics, the first time a climate scientist has received the award.

Climate model predictions developed by different research groups agree in many ways. For example, the ensemble of climate models used in the IPCC assessment agree that global surface temperature will rise under future emission scenarios and that the rise is linked to greenhouse gases. However, at a regional scale—over Michigan for example—agreement in the model often decreases, especially for some features, which reduces our confidence in the prediction. In response to a warming of 1.5 C, the models generally agree that Michigan will warm even more, by about 2-3 C, that the number of very hot days will increase, that mean precipitation will increase, and that the number of heavy precipitation events will increase. But the models don’t agree as much about other features, like the number of drought events.  

LSA: Reports such as the IPCC’s offer a lot of thresholds for gauging our relative progress or lack thereof. Many people feel dismayed by these reports because surpassing the thresholds can seem unavoidable and like it no longer matters what we do. But isn’t it true that every bit of carbon we do or don’t emit matters, and that the more carbon there is the more we have to remove and the worse things will get? Do individual actions ultimately make a difference? 

CP: Individual actions do matter. The U.S. has a population of 330 million people. If we all act individually to reduce our own emissions and hold our elected officials responsible for their decisions about our climate future, we will make a difference.

It is very easy to become fatalistic about climate change and to feel as though we’re acting too slowly and too late, especially given politicians’ inadequate response to the climate crisis. But we can’t give up. It is true that the carbon dioxide level in the atmosphere is the result of cumulative emissions and that every carbon dioxide molecule that humans emit will remain in the climate system for thousands of years on average. Further, the impacts of warming—heat waves, floods, droughts, glacial melting and sea level rise, species extinctions, and more—will increase in severity with additional warming, and the ability of the ocean and land to uptake CO2 and buffer the amount in the atmosphere is decreasing.

This is all to say that climate fatalism will doom us and future generations! We should do everything in our power to reduce emissions even while acknowledging that we’re not doing enough, fast enough.

LSA: What can the LSA community do to effect change?

CP: LSA has recently formed three working groups—with faculty, staff, and student participants—to answer this question and implement the recommendations of the President’s Commission on Carbon Neutrality. The three groups will focus on how LSA can reduce its carbon emissions from both on-campus and off-campus activities, and how it can leverage its research and education mission to reduce emissions beyond LSA. We’re incredibly excited about this work and look forward to seeing the working groups’ recommendations.