Real data — temperature, for instance — are almost always the combination of signal and noise, which we could also refer to as trend and fluctuation. Fluctuations are ubiquitous, they happen all the time. Sometimes they go up, sometimes down, sometimes a little and sometimes a lot,...
That’s why, even in a stable climate, we’re sure to see extremes. Heat waves will happen. So will floods, drought, and giant storms.
Temperature (and other weather variables), in addition to undergoing never-ending fluctuation, is also showing a trend — so the mean itself is changing. When that happens, a big fluctuation — not an extreme extreme, just an “ordinary” big one — gets added onto a higher mean value.
Fluctuation is only part of the story. When we add in the effect of trend, we get annual average temperature for the 48 contiguous states of the U.S.
... when that big fluctuation is added to the substantial trend, it is extreme. It’s more than trouble, it’s disaster. It’s crippling drought, deadly heat wave, a big dent in the corn crop, and terrible wildfires raging out of control.
Just this month, Australians experienced a similar large upward fluctuation in nationwide temperature. Again, all by itself that’s not such a big deal. Heat waves and wildfires happen, and since Australia is a pretty hot place anyway those who live there are well prepared for such fluctuations. But when they are added on top of a substantial trend
it becomes like nothing they’ve seen before. These data only go through 2011, they don’t include 2012 and certainly don’t show the astounding heat of early 2013. But they do reveal the trend, the increase in the average which makes every upward fluctuation far worse than it would have been.
The lesson is this: when trend and fluctuation collide, it creates unprecedented extremes. While extremes are trouble, unprecedented extremes are disaster.
Thanks also for the excellent cartoon (in the group comments) pointing out how climate change deniers try to mask the trends:
In the wake of Nemo in the Northeast US, PCCC has a petition to The Weather Channel, NBC, ABC, CBS, CNN, MSNBC, and other TV networks:
As consumers of news, we want you to report the truth about the historic blizzard hitting our country. It's a fact that climate change is making powerful and dangerous storms like this blizzard and Hurricane Sandy more likely, and Americans need you to report this fact in your coverage.