By Sue Smith-Heavenrich
This spring, members of the community are invited to join Cornell students and faculty in a series of seminars focusing on climate change. On Feb. 22, Art DeGaetano addressed the science and impacts of a changing climate. About 200 people filled the lecture hall, with an additional 50 or so participating via WebEx.
DeGaetano, a Professor in the Department of Earth and Atmospheric Sciences at Cornell, is also the director of the Northeast Regional Climate Center (NRCC) and serves as an editor for the American Meteorological Society Journal of Applied Meteorology and Climatology. His lecture focused on the physical science of climate and climate change impacts.
“When we talk about climate, we have to think about it as a system,” DeGaetano said. The earth, oceans, and atmosphere work together. Many things vary naturally, such as the intensity of the sun, El Niño cycles such as the one we’re currently experiencing, and volcanic eruptions. There are a number of human factors that affect climate too, including dust and aerosols, deforestation, and production of greenhouse gases.
Regardless of what factors are pushing climate change, the same basic laws apply. First, anything with a temperature above absolute zero emits radiation. Second, for a stable climate there has to be balance between the amount of energy coming from the sun and energy radiating back into space. It’s “climate change 101,” joked DeGaetano as he flipped to a slide showing an equation. He then proceeded to build a simple model of climate.
The neat thing about models—even simple ones—is that you can change one thing and see what happens to the climate. For example: greenhouse gases. Most of those come from burning fossil fuels, pushing ten billion tons of carbon into the atmosphere, said DeGaetano. Deforestation and aerial contrails make minimal contributions.
If you push a system too far in one direction, something happens. You get feedback, DeGaetano explained. For example, warming air melts ice and snow. That exposes more soil, providing more surface available to absorb, and radiate, the sun’s energy. Caught in the atmosphere, that heat contributes to increased warming, which melts more ice, which exposes more surface. “This is the reason polar regions are warming so much,” said DeGaetano.
Looking at data collected since 1980, it’s clear that the average global temperature has increased. “Twenty-fourteen broke records,” said DeGaetano. “So did 2015.” As for the future, if governments and corporations continue business as usual, the greenhouse gases will continue to rise. “No matter what we do this year, we’re locked into this climate change,” DeGaetano said. Looking at his models, he predicted that forty years from now, around 2050, the “coldest year” will be warmer than any of our previously recorded “warmest years”.
“So if you’re the governor, or the mayor of New York City, sea level rise is what you’re concerned with.” How far is that rise? Right now we’re talking about a foot, said DeGaetano. But with rapid ice melting, we could be looking at five feet. The impact from sea level rise depends a great deal on what infrastructure is built in low-lying coastal areas. The area around New York City includes gas storage areas, subway systems, nuclear power plants, all of which could be underwater.
Responding to a question, DeGaetano explained that it’s too early to tell whether we’re in a rapid ice melt scenario. “It’s a high-risk, low probability situation,” he said, “but if you’re thinking of building seawalls, this is definitely something you want to think about.”
Someone asked about the data and trends that climate deniers use to cast doubt on climate change science. “They cherry-pick their data,” said DeGaetano. “You can choose any period of time to show a trend.” For example, 2011 was much cooler than 2010. Then there’s local storms bringing snow and frigid air masses into an area. “Climate change doesn’t mean that the following year has to be warmer,” DeGaetano explained. There will be yearly variations; the important thing is the overall trend.
How many years does it take to know that you have a trend? Models, he said, can simulate the current system as well as simulate the future based on available data. “But,” DeGaetano cautioned, “you have to know your data. For example, historically the Ithaca thermometer used to be on a black roof. That affected the temperature readings.”
Another question arose regarding whether severe storms and chaotic weather were caused by climate change. “Linked, yes,” said DeGaetano, adding that it’s still too early to show causation.
The series of Monday afternoon climate seminars continues through May 9, excluding university holidays. The talks are held at 3:35 pm in room 233 of the Plant Science building on the Cornell University campus. Upcoming topics include the impacts of climate on food, water, land use, and economics. The lecture series is organized and sponsored by the Department of Biological and Environmental Engineering, the Cornell Institute for Climate Change and Agriculture, and the Atkinson Center for a Sustainable Future (www.acsf.cornell.edu/events/Climate2016.php).