Journal Article

Detectability of Post‐Net Zero Climate Changes and the Effects of Delay in Emissions Cessation

Borowiak, Alexander R., King, Andrew D., Maycock, Amanda C., Ziehn, Tilo, Alastrué de Asenjo, Eduardo, Clark, Spencer, Maher, Nicola

2025

Overview

There is growing interest in how the climate would change under net zero carbon dioxide emissions pathways as many nations aim to reach net zero in coming decades. In today's rapidly warming world, many changes in the climate are detectable, even in the presence of internal variability, but whether climate changes under net zero are expected to be detectable is less well understood. Here, we use a set of 1000‐year‐long net zero carbon dioxide emissions simulations branching from different points in the 21st century to examine detectability of large‐scale, regional and local climate changes as time passes under net zero emissions. We find that even after net zero, there are continued detectable changes to climate for centuries. While local changes and changes in extremes are more challenging to detect, Southern Hemisphere warming and Northern Hemisphere cooling become detectable at many locations within a few centuries under net zero emissions. We also study how detectable delays in achieving emissions cessation are across climate indices. We find that for global mean surface temperature and other large‐scale indices, such as Antarctic and Arctic sea ice extent, the effects of an additional 5 years of high greenhouse gas emissions are detectable. Such delays in emissions cessation result in significantly different local temperatures for most of the planet, and most of the global population. The long simulations used here help with identifying local climate change signals. Multi‐model frameworks will be useful to examine confidence in these changes and improve understanding of post‐net zero climate changes. Plain Language Summary The rapid pace of climate change is observed in many aspects of the Earth system including local warming and rainfall changes, increases in some extremes, and decreasing ice in polar regions. These observable climate change effects have been part of the motivation for the Paris Agreement and the push to achieve net zero emissions. There is a growing understanding that we should expect some aspects of the climate to continue changing under net zero and that there are benefits to getting to net zero sooner, but it has been unclear to date whether these changes will be obvious or masked by noise in the climate. Here we use simulations to examine how apparent climate changes may be under net zero and the effects of delays in achieving net zero. We find that over time, detectable changes in the climate system still occur under net zero. Many people live in places where we identify detectable local climate changes under net zero emissions. Delays in getting to net zero have identifiable effects across many aspects of the climate system. Achieving net zero should not be expected to halt all climate changes, but it is a necessary step in reducing climate change impacts. Key Points We examine detectability of global, regional and local climate change measures using millennial‐scale net zero CO2 emissions simulations Detectable changes under net zero are found in temperature and precipitation means and extremes, Atlantic Meridional Overturning Circulation recovery, and sea ice extent Delays to emissions cessation have widespread consequences for many centuries

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Arctic sea ice / Carbon dioxide / Carbon dioxide emissions / Climate / Climate change / Climate models / climate stabilization / climate variability / Climatic indexes / detection and attribution / Earth system modeling / Emissions / Global warming / Greenhouse gases / Local climates / Net zero / Northern Hemisphere / Precipitation / Sea ice / Simulation / Southern Hemisphere / Surface temperature / Temperature / Trends