The April 8 guest column by Rolf Westgard, “Global warming pause,” stated that global average temperatures have not risen appreciably since the late 1990s. Although Westgard is quite right that global warming appears to have slowed for the moment, ongoing research into its causes ought to be acknowledged. A growing number of scientists, including me, are driven to better understand the mechanisms that produce fluctuations in the pace of global warming.
Observational data from multiple climatic datasets show that the pause is primarily a wintertime phenomenon. While wintertime temperatures have remained constant over the oceans and even cooled over some land areas during the last decade, summertime temperatures have continued to rise, particularly over land. This fact has serious consequences for agriculture, ecosystems and human health.
In light of this more nuanced view of the hiatus, Westgard’s suggestion that society curtail investments in renewable energy appears misguided at best and extremely dangerous at worst for two key reasons.
That the rise in global temperatures has slowed over the past decade does not imply that global warming has stopped. The climate system is subject to both human and natural forces. While the human drivers of climate change continue to increase due to unabated greenhouse gas emissions, natural drivers of climate change fluctuate spontaneously in strength, at times accelerating global warming and at others counteracting it. It is plausible that the present pause in warming reflects a temporary cancellation of the human-induced warming by natural processes, such as variations in heat uptake by the deep ocean. Reducing investments in energy systems that emit less carbon would hamper our ability to control greenhouse gas emissions if the effect of natural variability reverses.
Moreover, the benefits of renewable energy extend beyond the outcomes that would accompany stabilized atmospheric greenhouse gas concentrations. According to the Union of Concerned Scientists, renewable energy sources emit less air and water pollutants than fossil fuels, impacting local environmental quality and public health for the better. In a warmer world, reductions in pollution associated with renewables would partially remedy human health losses related to more frequent heat-related illness.
As Twins fans continue to buy tickets at Target Field in spite of this week’s cool temperatures, so too should we continue to invest in carbon-free energy amid the current hiatus in global warming. Our understanding of the seasons assures us that summer is on its way, although we do not know precisely when it will arrive. Similarly, our knowledge of the climate system is sufficient to give us confidence that the pace of global warming will eventually increase, although we do not know exactly when or by how much. A lack of certainty is not a barrier to action. It drives scientists to discover and compels citizens to consider climate change as a risk worth addressing.