Tuesday, February 28, 2012

Warmer Winters, Fewer Freezes

This winter has been a warm one, but it isn't in the top ten just yet.  As of Tuesday, February 28, 2012, this winter ranks as the 11th warmest.  It might edge into the top ten thanks to a leap year.

Winters have been warming over the past few decades nationwide.  Here in South Carolina the winters have warm about 2 degrees F over the past 35 years.  The South has always enjoyed milder winters, but this has been more so lately in spite of the last two winters.

This map shows the average winter temperature trend 1976-2010.  Image Credit: Climate Central.

The warming has had benefits and problems.  Problems have included more summer insects, fewer chilling hours for peaches, and drier conditions.  However, one of the benefits has been a longer growing season.  The growing season has expanded by one week in the Midlands over the past 35 years.

The number of below freezing days in Columbia.  To see the interactive graphic, click here.  Image Credit: Climate Central.

There are all sorts of ways to gauge whether the climate is changing, and how. One is to look at the number of days where the temperature dips below freezing in each calendar year. In Columbia, that number has been going down since 1960—with some big swings, but with a downward trend overall. Fewer freezing days implies a warming climate. The blue dotted line in the chart above represents a 25-year average of data from individual years. So the dot for 1990, for example, is an average of the data from that year, the previous 12 and the 12 that came after. That’s why the blue line starts later, and ends earlier, than the overall trend line.

The chart shows data for individual years, for the 25-year average, and for the overall linear trend. By clicking on the link in the caption, you can go to an interactive version where you can switch the individual components on or off.

It is still too early to plant.  The average last freeze is around the last week in March for the Midlands.  This is the time to prepare the garden for planting.  The latest freeze on record is April 24, but this year the growing season is likely to get underway much earlier.  Stay tuned!