Temperatures on the Eastern seaboard have risen to the high 80s and low 90s in recent days, 20 to 30 degrees Fahrenheit above normal for April in the region. Here in New York City, where Scientific American's offices are located, we may break the record high of 90 degrees Fahrenheit on this date set back in 1990. But as the temperature climbs in the Northeast and summer wilt sets in before trees have even budded out, it's worth remembering that weather is not climate.

Weather is the day-to-day temperature, humidity or precipitation that determines whether you'll wear your spring coat or strip down for summer. Climate is the overall combination of all these elements over a long period of time.

Temperature records kept since the 19th century reveal that global average temperatures are inexorably creeping up, a phenomenon dubbed climate change. The cause? Increasing levels of greenhouse gases, most commonly carbon dioxide, in the atmosphere, which trap heat that would otherwise radiate back out to space, like a smothering blanket.

The effects of such climate change range from increasing extreme weather events (droughts to downpours) to subtly shifting forward the change of seasons from winter to spring, for example.

But that doesn't mean that climate change can be blamed for any given weather event, like this hot spell that may set high temperature records in New York City, among other places. Weather is too inherently variable to be blamed on any one thing (as the old saying in my home state of Missouri goes: "If you don't like the weather, wait five minutes and it'll change.")

Of course, it doesn't hurt to have record high temperatures as negotiators from the world's major economies meet in Washington, D.C. to discuss global efforts to combat climate change. Just remember, no individual weather event—from Hurricane Katrina to an early spring heat wave—can be conclusively tied to global warming. Only when you bundle them all together can you begin to see the picture of a climate that is changing.

Credit: © iStockphoto.com / Nick M. Do