I’m a believer in climate change because of the book Storms of My Grandchildren, by James Hansen, that I read a few years ago. For those of you not familiar with Hansen, he is the director of NASA’s Goddard Institute for Space Studies and adjunct professor in the Department of Earth and Environmental Sciences at Columbia University. He is also an alumnus of the University of Iowa and has testified before Congress on climate change.

To better understand the concept of climate change, two terms that Hansen uses a lot — climate-change forcings and climate-change feedbacks — need to be clarified. “Forcings drive climate change. Feedbacks determine the magnitude of the climate change.”

The main human-made forcing on Earth is the greenhouse-gas carbon dioxide (CO2) that comes from burning fossil fuels such as coal, oil, and gas. Since human beings started burning these fuels in large quantities, CO2 has accumulated more quickly and at higher levels as measured in parts per million (ppm) compared to preindustrial age accumulations.

During glacial-interglacial cycles, CO2 levels topped out at less than 300 ppm. Now, we are approaching levels of 390 ppm. Higher levels of CO2 mean that the Earth radiates less heat back into space than what it absorbs from the sun. Over the last 100 years, the average global temperature has increased by 1.5 degrees Fahrenheit.

The most important feedbacks “… all involve water, in either its solid, liquid, or gas form.” Glaciers, for instance, help cool our planet because they reflect back to space most of the sunlight that hits them, but bodies of water and water vapor absorb heat, and a warmer planet leads to a higher probability of more extreme weather events, such as droughts and heat waves as well as heavier rains and intense storms.

The speed at which our planet is warming is disturbing. Visual evidence of this warming can be seen in the film Chasing Ice, which will be shown at the Bijou from March 8-14.

Iowa City’s Landlocked Film Festival is proud to be a cosponsor of this film.

Susan Moore