Abrupt Climate Change in a Warming World
Early last month, I attended a meeting on Abrupt Climate Change in a Warming World. Climate Matters @ Columbia has discussed abrupt climate change before, referring to the hydrologic cycle, and with regards to melting sea ice or permafrost.
Shifts in the earth climate are a known fact: crocodile-like reptiles lived in Greenland 55 million years ago while ice covered Manhattan and London around 20 thousand years ago. The climate system is complex, and like many complex systems, there is a tendency to reside in a given state, such as with ice or without. As humans burn fossil fuels and change land cover, we increase atmospheric levels of greenhouse gases that warm the planet. Shifts between different states may be triggered by this warming trend.
When do we consider climate change abrupt? Remembering that climate represents the weather conditions over a period of about 30 years, a change in climate is considered abrupt when it takes place over a comparable period.
Among the multiple definitions of abrupt climate change, it can be useful to refer not so much to the precise length of time, but rather to the time required for human systems to adapt. While climate has changed abruptly in the earth’s past, things are fundamentally different today, primarily because there are presently over 6 billion people on the planet. Humans inevitably use water, clear forests to grow food and build cities, and in turn they will be affected by changes in the patterns of precipitation, the progression of seasons, and in the number of frost-free nights and of heat waves.
One way to think about it is that going from the climate of New York City, with summer highs of 83F and winter lows of 23F and maximum precipitation in May of 4.5 inches, to that of Atlanta, with summer highs of 89F and winter lows of 33F and peak rainfall in March of 5.4 inches, over 1000 years or in 10 years. If the shift were to happen in 10 years, dealing with heavier precipitation at a different time of year and likely increased use of air conditioners would be a burden for NYC infrastructure, such as the subway system and the electric grid.
A group of researchers at the Lamont-Doherty Earth Observatory have been studying abrupt climate change for several years. They currently have a project aiming to look at past, present and future climate in the context of anthropogenic warming. The July meeting brought together researchers from Lamont, Columbia and elsewhere to discuss several aspects of abrupt change and how they interact and affect society.
Shifting precipitation patterns, the speed of ice loss in Greenland, past and present drivers of atmospheric carbon dioxide, glacier retreat, tropical cyclones, the role of climate in the spread of malaria, the challenges of water management, and threats to food security were a few of the many topics covered at the meeting.
One of the clearest messages was that the only way we can begin to understand what might occur in the future is by studying the past. Models can only address those processes and interactions that we understand. It is crucial to improve the tools used to quantify past climate conditions. Then, by trying to model the record of past climate, new relationships and processes are revealed.
You can read the summary of the talks and see several of the presentations here. And stay tuned for more posts on abrupt climate change.