Climate Change in Vermont

Vermont’s climate has changed substantially in the past fifty years. Continuing change is certain, as the Earth’s climate is being driven towards a warmer state by the increase of greenhouse gases in the atmosphere. The primary driver is the increase of atmospheric CO2 from the burning of fossil fuels, which reduces the cooling of the Earth to space. The small warming from the increase of CO2 is amplified several times(1) because atmospheric water vapor, another powerful greenhouse gas, increases as temperature increases. Reductions in snow and sea-ice cover at northern latitudes also amplify the warming, because less of the sun’s energy is reflected.

We have two complementary reference frameworks when planning for the future:

1) Regional projections from climate models

2) Climate trends in Vermont and New England in recent decades

Global model projections help us look into an uncertain future and explore humanity’s options. For example, we can estimate how the patterns of temperature and precipitation will change, and see how reducing greenhouse gas emissions give a smaller temperature rise by the end of this century. Our models for the Earth’s climate system necessarily contain simplifications, but they are continually revised as understanding improves. In 2007, a major synthesis was completed by an international team of 500 lead authors and 2,000 expert reviewers for the Intergovernmental Panel on Climate Change. This Fourth Assessment Report (IPCC-AR4)(2) documented the global and regional changes in temperature and precipitation expected this century. This report contains results from regional studies for the United States and New England that were based on the IPCC-AR4 report. Some 800 experts are now working on the next update, the Fifth Assessment Report, expected to be finished in 2014.

Our biggest challenge is that our ability to predict the future climate in detail is limited. So it is very helpful to examine climate trends in Vermont and New England in recent decades as a guide for the future. These recent observational trends are familiar to local communities and can help us understand the relationship between the local climate change that we are experiencing and projected global climate changes.