Has spring sprung a week earlier than 15 years ago?
That's what Boston University researchers say.
Using global satellite data, Myneni claims to have detected an earlier rise in photosynthetic activity in the northern latitudes between 1981 and 1991. Photosynthesis is the process by which plants use sunlight to make carbohydrates.
The researchers claim the earlier rise in photosynthesis is indicated by an increase in something called the "normalized difference vegetation index" (NDVI) — a number that is calculated from satellite measurements of solar radiation reflected by green plants.
So is spring coming earlier? Well, don't plan on moving your tomatoes outside in February just yet.
As the accompanying Nature editorial put it:
Should we believe the NDVI trend? There are no "ground-truth" measurements of photosynthesis at northern high latitudes over the same period, and so the accuracy of the trend cannot be established unambiguously.
But what really bothered me was the following graph supposedly showing an earlier increase in the NDVI.
The single line to the left represents the NDVI for 1989-1990. The lines to the right (that are too jumbled to distinguish one from another) are the NDVIs for 1982-1983, 1985-1986 and 1987- 1988.
Okay, so the 1989-1990 NDVI increased earlier than the NDVI for the other periods. So what! It's only 1989-1990. Hardly a trend!
And look at what's missing from Myneni's graph — data for the year 1984. What happened? Was there no photosynthesis in 1984? Did 1984 not happen at all? Or did the researchers not like data? According to the researchers,
Data from 1984 were not included because the number of years was odd.
Odd? I think the only thing that is odd is Myneni's explanation.
Finally, The Washington Post's headline for this article proclaimed Climate Report Shows Longer Growing Season, Heats up Debate Over Global Warming. The implication being manmade greenhouse gases have caused spring to come a week earlier.
But even the researchers acknowledge that
The winter and spring warming in the interior of the continents of Asia and North America in the 1980s may be a result of natural causes not yet explained...
And the accompanying editorial started out,
For whatever reasons, the period since 1980 has been the warmest in the past 200 years. [Emphasis added]
Regardless of whether spring has sprung a week earlier (and this study is not convincing evidence of that), there certainly is no link with manmade emissions of greenhouse gases.
And do you think these Boston University researchers might feel just a little silly since this was the headline in the Boston Globe on April 1, 1997:Blizzard Leaves Many Powerless
The headline refers to the 30+ inches of snow dumped on Boston after spring began!