Seasons have changed, it’s the human fingerprint on climate

Human beings are changing seasonal cycles in the lower atmosphere: it’s the result revealed by nearly four decades of global temperature data collected by satellites, a study on Science highlights.

Increase in global annual temperatures, growing heat content of the oceans, the melting of the polar ice sheets and glaciers causing sea level rise: anthropogenic climate change has become clearly observable through many metrics. But human beings have profound impacts on climate, not only in the annual temperatures but also in the seasonal cycle. 
A study recently published on Science (and commented here on Nature) highlights this noteworthy result: an analysis of decades of satellite data has revealed how humans are changing seasonal cycles in the lower atmosphere while highlighting how the accumulation of greenhouse gases produced by burning fossil fuels has increased temperatures in summer and caused larger annual temperature swings in the northern hemisphere.

The study, lead by author Benjamin Santer, an atmospheric scientist at the Lawrence Livermore National Laboratory in California, is the first to pinpoint human influences in the seasonal cycle changes in the atmosphere while clearly highlighting the atmospheric fingerprint of climate change.

Enlarge

F1.large_
Trends in the amplitude of the annual cycle of tropospheric temperature.
Trends are calculated over 1979 to 2016 and are averages from a large multimodel ensemble of historical simulations. The most prominent features are pronounced mid-latitude increases in annual cycle amplitude (shown in red) in both hemispheres. Similar mid-latitude increases occur in satellite temperature data. Trends are superimposed on NASA’s “blue marble” image.

Science

Researchers were interested in the geographical pattern of the amplitude of the annual cycle of tropospheric temperature: information on how this temperature has changed over time is available from satellite data and from large multi-model ensembles of simulations. Therefore Santer’s team used computer models to simulate the global climate over thousands of years, with and without greenhouse-gas emissions. This allowed them to highlight what they called the “fingerprints” of human influence on atmospheric conditions. The patterns were then compared with satellite temperature data collected since 1979 while revealing that natural variations in Earth’s climate could not account for all of the observed changes in seasonal climate cycles.
The most significant change was in the northern hemisphere, where the difference between summer and winter temperatures has increased by around 0.4 °C, mostly due to the fact that summer temperatures are rising more quickly.

Read more:
The study on Science: Santer, B. D. et al. Science 361, eaas8806 (2018).

The news published on Nature.

The comment of Antonio Navarra, President of the CMCC Foundation (in Italian language only).

Share

Article

Food for Climate

Two faces of the same world. Obesity, food loss and waste, land competition for non-food crops on the one hand. Hunger, struggle for food security, worries for a growing population to feed on the other hand. Many paradoxes are governing the current unsustainable food system, grounded in a type of agriculture that maximizes yields at any cost for human health and the environment. We dive into an open debate in the scientific community about how to ensure that the agriculture of the future is sustainable and good for the climate, analyzing the pros and cons of organic farming as a possible solution.

Article

Filling in the Climate Reporting Gap

They build capacity and offer a voice for the areas which are most affected by Climate Change. They create a broad and fluid network of journalists and communicators that share resources, information and opportunities. All of which, in a very effective and innovative way. Discover Climate Tracker, the next generation of climate journalists.

Article

Biodiversity continues to decline

The value of ecosystem services is estimated at $125 trillion, just a few trillion less than the world’s total GDP, yet we are failing to …