A new climate report suggests that the extreme weather patterns seen in the U.S. this year- flooding, heat waves, drought, heavy rain- may have been partly caused by global warming.

The Current Extreme Weather & Climate Change report was released on Friday by Climate Communication, a non-profit science and outreach project.

The project involved researchers from the National Center for Atmospheric Research, Weather Underground, and the Scripps Institution of Oceanography.

Greenhouse gases are the steroids of weather, Jerry Meehl of the NCAR said at a news conference.

And it doesn't take much for a big change to happen.

Small changes in the averages of many key climate variables can correspond to large changes in weather, the study's overview says. Substantial changes in the frequency and intensity of extreme events can result from a relatively small shift in the average of a distribution of temperatures, precipitation, or other climate variables.

The study's overview on the CC Web site notes that extreme weather can harm ecosystems, as well as interfere with human activities such as food production and water management.

A warmer atmosphere has more energy to power storms, reviewer Jeff Masters of WU said at the news conference. Years like 2011 may be the new normal.