Earth's seasons now arrive 2 days earlier, researchers report

Jan 21, 2009

(PhysOrg.com) -- Not only has the average global temperature increased in the past 50 years, but the hottest day of the year has shifted nearly two days earlier, according to a new study by scientists from the University of California, Berkeley, and Harvard University.

Just as human-generated greenhouse gases appear to the be the cause of global warming, human activity may also be the cause of the shift in the cycle of seasons, according to Alexander R. Stine, a graduate student in UC Berkeley's Department of Earth and Planetary Science and first author of the report.

"We see 100 years where there is a very natural pattern of variability, and then we see a large departure from that pattern at the same time as global mean temperatures start increasing, which makes us suspect that there's a human role here," he said.

Although the cause of this seasonal shift - which has occurred over land, but not the ocean - is unclear, the researchers say the shift appears to be related, in part, to a particular pattern of winds that also has been changing over the same time period. This pattern of atmospheric circulation, known as the Northern Annular Mode, is the most important wind pattern for controlling why one winter in the Northern Hemisphere is different from another. The researchers found that the mode also is important in controlling the arrival of the seasons each year.

Whatever the cause, Stine said, current Intergovernmental Panel on Climate Change (IPCC) models do not predict this phase shift in the annual temperature cycle.

Details are published in the Jan. 22 issue of the journal Nature.

Temperatures at any given time of the year can be very different on land than over the ocean, Stine said, and a change in the strength and direction of the winds can move a lot of heat from the ocean onto land, which may affect the timing of the seasons. However, this seems to be only a partial explanation, he said, because the relationship between this pattern of circulation and the shift in the timing of the seasons is not strong enough to explain the magnitude of the seasonal shift.

The researchers also found that the difference between summer and winter land temperatures has decreased over the same 50-year period, with winter temperatures warming more than those in summer. They found that in non-tropical regions, winter temperatures over land warmed by 1.8 degrees Celsius and summer temperatures increased by 1 degree. Ocean warming has been somewhat less.

Stine noted that the study limited its focus to non-tropical regions because the seasons are more pronounced outside the tropics.

Stine, Peter Huybers, assistant professor of earth and planetary sciences at Harvard University, and Inez Fung, UC Berkeley professor of earth and planetary science and of environmental science, policy and management, and co-director of the Berkeley Institute of the Environment, based their study on a publicly available database of global surface temperature measurements over both land and ocean from 1850 to 2007 that was compiled by the University of East Anglia's Climate Research Unit in the United Kingdom. Using non-tropical data only, the team found that, while land temperatures in the 100-year period between 1850 and 1950 showed a simple pattern of variability, with the hottest day of the year in the Northern Hemisphere around July 21, temperatures in the period 1954-2007 peaked 1.7 days earlier.

Stine said that monthly temperatures follow a sinusoidal curve, rising to a peak in mid-summer, then dropping to a winter low, and finally rising again because of increased sunshine to another summer high. The temperature typically lags solar insolation by about 30 days over land and 60 days over the ocean, he said, because it takes less energy to heat the moisture in soil than to heat the ocean.

Biologists have noticed large changes in the arrival time of many signs of spring over the past 50 years. Buds have been seen opening earlier, birds migrating earlier, snow melting earlier and sea ice breaking up earlier. These changes have been explained by the fact that the Earth is warming, and thus the temperature in any given month has increased. In contrast, this new study finds that individual months have been warming at different rates than others, and that as a result, the peak summer temperature and lowest winter temperature both now come earlier in the calendar year.

"We're saying that, on top of the long term trend of warmer summer and winter highs, peak warming is coming earlier within the year," Fung said. "It's not just the onset of spring, but the peak."

The research team is now looking for other mechanisms to explain the observed shift in the timing of the seasons. These include a hypothesized drying of the global soils, which would cause the land surface to respond more quickly to the sun, and changes in the amount of solar energy absorbed by the atmosphere due to industrial pollution.

One surprising aspect of the researchers' findings is that the changes they discuss explain so much about the changes over the last 50 years in the month-to-month pattern of temperatures around the globe.

"Once we have accounted for the fact that the temperature averaged over any given year is increasing, we find that some months have been warming more than other months. We were surprised to find that over land, most of the difference in the warming of one month relative to another is simply the result of this shift in the timing of the seasons, and a decrease in the difference between summer and winter temperatures," said Stine.

"The difference between summer and winter temperatures is comparable to the difference between ice age temperatures and non-ice age temperatures over much of the planet," Stine said. "Thus, small changes in the annual cycle can produce a big effect even if they do not change the annual mean temperature."

Provided by University of California - Berkeley

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User comments : 11

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morpheus2012
2.1 / 5 (16) Jan 21, 2009
world elite kiked in to to high gear on the global warming scam now taht obama is in office before

carbon tax on people and catle aka they will tax
cow pigs on how much they fart ofcourse this will be payed by owner of those beeings

u cant make this up

http://www.youtub...hY17F_1s
Entropic_Dreaming
2.5 / 5 (15) Jan 21, 2009
I'm tired of all these global warming alarmists stories. Perhaps reporters on physorg could come up with something a bit more pertinant and scientific. What will they do next? "NEW POLL AMONG HISTORIANS SHOWS THAT THE 100 YEAR WAR WAS IN FACT 3 DAYS LONGER THAN PREVIOUSLY THOUGHT"

It's really quite silly to see such nonsense among real developements in nanotechnology and energy and physics.
gmurphy
3.1 / 5 (12) Jan 21, 2009
Entropic_Dreaming, this article is not alarmist, it makes no threatening claims. Personally, I'm tired of reading posts by scientific bigots whose highest aspiration in life is to smear hard won scientific insight with the same old tired labels: "alarmist", "propaganda" or "fraud". Of course it could be Al Gore making all the scientists write these papers, you'd better go and prepare some tinfoil hats, just in case :-P
dachpyarvile
2.3 / 5 (12) Jan 21, 2009
And, yet, in my neck of the woods birds were observed migrating south for the winter nearly a month early, as did migratory bats. How does that relate to this "new" so-called observation? :)
vlam67
3.4 / 5 (9) Jan 21, 2009
Interesting that as soon as "global" and "warming" appear anywhere on the Net there are score of humans start foaming at the mouth. I am amazed at their efficiency.
MikeB
2.5 / 5 (6) Jan 21, 2009
This is the way we have been taught to see temperatures by anomalies:

http://zapruder.n...3qk7.gif

If you notice, the difference between about 1980 and now is less than a degree... Oh yes this is even WITH Hansen's adjustments.


THIS is the way we SHOULD be looking at temperatures. We should look at the actual monthly temperatures:

http://junkscienc...lute.gif

The problem is, you see, the temperatures are not really that scary if you see the actual global temperatures instead of an anomoly graph. The actual temperatures are much more instructive.
paulthebassguy
1.7 / 5 (11) Jan 21, 2009
I thought that seasons were caused by the angle of the earth, and the orbit around the sun - how could human activity possibly affect that?!?!?
Soylent
5 / 5 (2) Jan 22, 2009
And, yet, in my neck of the woods birds were observed migrating south for the winter nearly a month early, as did migratory bats. How does that relate to this "new" so-called observation? :)


It doesn't.
MikeB
3.3 / 5 (3) Jan 22, 2009
And, yet, in my neck of the woods birds were observed migrating south for the winter nearly a month early, as did migratory bats. How does that relate to this "new" so-called observation? :)


Well, the headline says, "Earth's seasons now arrive 2 days earlier, researchers report", so I guess all the seasons, with an "s", are 1.7 days earlier. Maybe someone should tell that to the migrating birds. The birds seem to think winter is earlier than the researchers say.
VinceCataldi
not rated yet Jan 22, 2009
"Seek, and you shall find!"; or science?
DeadCorpse
2.2 / 5 (13) Jan 22, 2009
Any "theory" that fails to account for the last 4-5 glaciation events is bunk. Including all the so-called "science" around anthropogenic global climate change.

http://www.seed.s...emp2.jpg

According to that last 400,000 years worth of data, we still have another 2-3 degrees to warm up before our next scheduled drop off. Get back to us in a couple thousand years and let us know how it turned out.
GrayMouser
1.6 / 5 (7) Jan 23, 2009
If the hottest day is coming 2 days earlier, instead of it being hotter for 2 days longer, I would say it is orbital precession instead of some mythical AGW.