UV exposure has increased over the last 30 years, but stabilized since the mid-1990s
From NASA Goddard press release here
NASA scientists analyzing 30 years of satellite data have found that the amount of ultraviolet (UV) radiation reaching Earth’s surface has increased markedly over the last three decades. Most of the increase has occurred in the mid-and-high latitudes, and there’s been little or no increase in tropical regions.
The new analysis shows, for example, that at one line of latitude — 32.5 degrees — a line that runs through central Texas in the northern hemisphere and the country of Uruguay in the southern hemisphere, 305 nanometer UV levels have gone up by some 6 percent on average since 1979.
The primary culprit: decreasing levels of stratospheric ozone, a colorless gas that acts as Earth’s natural sunscreen by shielding the surface from damaging UV radiation.
The finding reinforces previous observations that show UV levels are stabilizing after countries began signing an international treaty that limited the emissions of ozone-depleting gases in 1987. The study also shows that increased cloudiness in the southern hemisphere over the 30-year period has impacted UV.
Jay Herman, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md., stitched together data from several earth observing satellites — including NASA’s Aura satellite, NOAA weather satellites, and commercial satellites — to draw his conclusions. The results were published in the Journal of Geophysical Research in February.
“Overall, we’re still not where we’d like to be with ozone, but we’re on the right track,” said Jay Herman. “We do still see an increase in UV on a 30-year timescale, but it’s moderate, it could have been worse, and it appears to have leveled off.”
In the tropics, the increase has been minimal, but in the mid-latitudes it has been more obvious. During the summer, for example, UV has increased by more than 20 percent in Patagonia and the southern portions of South America. It has risen by nearly 10 percent in Buenos Aires, a city that’s about the same distance from the equator as Little Rock, Ark. At Washington, D.C.’s latitude — about 35 degrees north — UV has increased by about 9 percent since 1979.
The southern hemisphere tends to have more UV exposure because of the ozone hole, a seasonal depletion of the ozone layer centered on the South Pole. There are also fewer particles of air pollution — which help block UV — due to the comparatively small numbers of people who live in the southern hemisphere.
Despite the overall increases, there are clear signs that ultraviolet radiation levels are on the verge of falling. Herman’s analysis, which is in agreement with a World Meteorological Report published in recent years, shows that decreases in ozone and corresponding increases in UV irradiance leveled off in the mid-nineties.
The Many Sides of Radiation
Shorter ultraviolet wavelengths of light contain more energy than the infrared or visible portions of sunlight that reach Earth’s surface. Because of this, UV photons can break atmospheric chemical bonds and cause complex health effects.
Longer wavelengths (from 320 to 400 nanometers) — called UV-A — cause sunburn and cataracts. Yet, UV-A can also improve health by spurring the production of Vitamin D, a substance that’s critical for calcium absorption in bones and that helps stave off a variety of chronic diseases.
UV-B, which has slightly shorter wavelengths (from 320 to 290 nanometers), damages DNA by tangling and distorting its ladder-like structure, causing a range of health problems such as skin cancer and diseases affecting the immune system.
As part of his study, Herman developed a mathematical technique to quantify the biological impacts of UV exposure. He examined and calculated how changing levels of ozone and ultraviolet irradiance affect life. For Greenbelt, Md., for example, he calculated that a 7 percent increase in UV yielded a 4.4 percent increase in the damage to skin, a 4.8 percent increase in damage to DNA, a 5 percent increase in Vitamin D production, and less than a percent of increase in plant growth.
“If you go to the beach these days, you’re at slightly higher risk of getting skin cancer (without protection),” Herman said, though he noted the risk would have been even greater in the absence of regulations on ozone-depleting substances.
Last year, one of Herman’s Goddard colleagues, Paul Newman, published a study showing that the ozone hole likely would have become a year-round fixture and UV radiation would increase 650 percent by 2065 in mid-latitude cities if not for the Montreal Protocol, an international treaty signed in 1987 that limited the amount of ozone-depleting gases countries could emit.
Clouds and Hemispheric Dimming
In addition to analyzing ozone and ultraviolet trends, Herman also used satellite data to study whether changes in cloudiness have affected UV trends. To his surprise, he found that increased cloudiness in the southern hemisphere produced a dimming effect that increased the shielding from UV compared to previous years.
In the higher latitudes especially, he detected a slight reduction — typically of 2 to 4 percent — in the amount of UV passing through the atmosphere and reaching the surface due to clouds. “It’s not a large amount, but it’s intriguing,” Herman said. “We aren’t sure what’s behind it yet.”
Vitali Fioletov, a Canadian scientist and member of the World Meteorological Organization’s advisory group on ultraviolet radiation, agreed that Herman’s findings about cloudiness warrant additional investigation. “I found the cloud effects on the global scale to be the most interesting aspect of the study,” he said. “This isn’t something you could see without satellites.”
Herman synthesized measurements from the Total Ozone Mapping Spectrometer (TOMS) aboard Nimbus 7 and Earth Probe, the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite, NASA’s Sea-Viewing Wide Field-of-view sensor (SeaWiFS) on the commercial SeaStar satellite, and the Solar Backscatter Ultraviolet Instrument (SBUV) on several polar orbiting NOAA weather satellites.
Related Links:
Global increase in UV irradiance during the past 30 years (1979–2008) estimated from satellite data
h/t to Dr. Leif Svalgaard
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Not fixed! 32.5 degrees North latitude runs through central Texas; 32.5 degrees South latitude runs through Uruguay.
Texas and Uruguay don’t share any longitudes. Uruguay is entirely (hundreds of miles) east of any point in the United States.
They start of talking ofsatellite data, but then discuss surface UV levels. I think a little more explroation is in order. How has the Sun’s UV output varied over this period?
So, UV increased over the last 30 odd years, than in the last few years cloudiness has increased to counter it. If ozone changes are primarily driven by the solar cycle as some now believe, this could further support a number of theories about solar activity heating (and now cooling) the climate.
What interests me in the IPCC in their circular logic is that they blame 100% of the warming over the last 30 years on man – but this suggest it was due to an increase in incoming solar energy (which can still be blamed on man by some, CFC’s, reduction of black soot etc…) but what it does show is co2 may have played much less of a role than they claim – infact I wonder how much w/m2 increase that is due to UV, and if co2 can account for anything with this data? The recent increase in cloudiness is also evidence of a negative feeback to control warming, and counters the IPCC theory of strong positive feedbacks
A C Osborn (11:35:10) : A good link: http://virtualacademia.com/pdf/cli267_293.pdf
I ask for an indulgence here (It is ozone related)— Everyone seems focused on climate change and EPA is using this opportunity to release new and very costly ground level ozone regulations. The largest source of ground level ozone precursors are soil bacteria NOx and isoprenes from trees. Energy related emissions and local climate are considerations in urban areas however what EPA is trying to do is to remove any context by which urban and “natural” ground level ozone may be compared. Ground level ozone levels in many of our national forests will exceed EPAs new standards– to avoid this inconvenient fact EPA will not monitor for ozone where natural background levels will exceed standards— and as such all ozone violations are anthropogenic. It is a time proven EPA strategy. And the next time someone says we need to plant trees in urban areas to reduce CO2 — ask them about the increase in tree smog from isoprenes.
Re: gcb (Mar 17 11:32),
Cabriolet is another name for a soft-top convertible.
Also known as “rag tops” to the colonials over here.
Apart from the suspect use of satellites to record UV at the surface (as someone else has noted above) this is an “Average” again. Like Global temperature, such averages are highly suspect.
Ozone hasn’t increased uniformly since 1979, but goes through a highly variable annual cycle, and also varies with the solar cycle.
Its the sort of research produced by social scientists, who treat scientific data like consumer preferences!
Re: R. Gates (Mar 17 09:52),
More to the point, the damage done to the ozone layer was serious, did increase UV, but we caught it in time and did something about it. It did prove that humans can both cause and solve problems on a global scale. In as much as AGW is a problem, hope can be found in this example.
R. Gates,
The difference is that the “precautionary principle” applied to CFC use was not remotely as expensive and disruptive as the proposed CO2 emission reductions. I think the real lesson comes from the AGW fiasco and the destruction of trust in the scientific process. When AGW is put to rest, one way or another, it might be worth revisiting the CFC/ozone thing. In retrospect, the CFC scare looks too much like a practice run for the main event, climate change.
1. How did they measure UV levels? Did they actually measure them at ground level, just infer them from satellite-measured ozone levels, or make them up on the spot?
2. As usual, mankind has been blamed, this time for what might be natural cyclical changes in ozone concentration. Has there ever been a direct measurement of Freon-12 molecules in the ozone layer?
And then we have the usual question!
How does the ozone holes history look like?? This is thirty years…only.
The curve say what? Maby its lower than ever or…higher than ever!
Who knows?? Nobody!!!
Michael not Mann (09:40:37) :
“They’ve been shining UV all over the place looking for rouge sperm.”
Sounds like a serious medical issue!
It should be noted that you can offset the increase in UV by moving a few dozen kilometers polewards as long as you avoid the southern hemisphere ozone hole. The closer you get to the poles, the lower the UV insolation because UV doesn’t make it unscattered through many kilometers of atmosphere. That’s why Germany or southern Canada have a practically UV-free winter; you won’t produce any Vitamin D on winter days even when there are no clouds. Björn Lomborg has numbers on this in “The Skeptical Environmentalist” but i don’t have my copy at hand.
This is also the reason why fair skinned people developed in northern countries; they are better in absorbing UV. So when determining your optimal habitat, take your complexion into account.
Slabadang> How does the ozone holes history look like?? This is thirty years…only. The curve say what? Maby its lower than ever or…higher than ever!
Who knows?? Nobody!!!
I bet Michael Mann could produce a 2000 year graph of the ozone hole’s history based upon a single tree in his back yard.
Doesn’t uv heat ozone? When ozone levels were dropping, wouldn’t it make sense for more uv to make it through the stratosphere to the earth’s surface? As ozone replenished in recent years, wouldn’t that decrease the amount of uv that gets to the surface of the earth?
“What the hell is a Cabriolet?! Some kind of goofy French car?”
The Cabriolet
http://www.wired.com/images/article/full/2007/09/porsche_911_630x.jpg
I suspect that total UV rays energy isn’t sufficient to cause significant warming, but it has enough impact to cause increase rate of the skin cancer occurrences. If so, it would also affect phytoplankton, as I suggested some time ago. Ana pointed out that phytoplankton indeed has a mechanism to fight back. However this may not be efficient enough if increase is above normal (evolution mechanisms are slow to develop).
There also may be a side effect to this phenomena, if plankton is sterilised or even destroyed (result is the same), than transparency of the ocean surface layers (where phytoplankton can normally would be found, would be increased.
Incoming TSI of 1365 W/m^2 instead of being absorbed in the few feet at the top (where the plankton reduces transparency) and proportion of it radiated back into air, it may penetrate good number of meters further down, less heath in the surface, more further down, consequently the loss due to radiation back into space will be reduced, more heath retained in the oceans.
Does this make sense?
I am deeply suspicious. If you look at the Antarctic ozone ‘hole’ data:
http://ozonewatch.gsfc.nasa.gov/index.html
it appears that signing the Montreal Protocol in 1990 was already too late. The ozone ‘hole’ had already reached nearly 20Mkm^2 in 1987 – not far off the 20-25Mkm^2 it has been for the last 20 years.
Don Keiller (09:37:41) already mentioned that there may be a problem with the assumed cause of the ‘hole’.
I think the NASA report may have more to do with attempting to show that international action can solve ‘global’ problems – like R. Gates (09:52:36) seems to think it can.
Call me skeptical but I don’t think the Montreal Protocol had any, or will have any, effect on the Antarctic ozone ‘hole’.
I’ve read, http://www.scienceagogo.com/news/20040614015421data_trunc_sys.shtml, that increased uv contributes to increased cloud formation. Isn’t that consistent with the report of increased clouds in the southern hemisphere when ozone declined in the 80’s?
So does the ozone layer strength have a significant impact on cloud formation (i.e. less ozone => more uv into the troposphere => more clouds)?
I am confused by the wording of the press release. UV goes up and the culprit is decreasing levels of stratospheric ozone and then the rest seems to say we’re on the right track.
We’ve discussed the “ozone hole” here before. One of the largest holes ever was just a few years ago – have a look at the largest ozone hole ever observed – on 24 September 2006.
http://ozonewatch.gsfc.nasa.gov/daily.php?date=2006-09-24
And the same sorts of bad science was going on back when this issue was the scare of the week:
http://www3.interscience.wiley.com/journal/13749/abstract?CRETRY=1&SRETRY=0
But, of course, the science is settled.
R. Gates
Acid Rain was the “practice run” for climate change. It relied on models based on erroneous assumptions. It named the crisis after a natural phenomena-as all rain is by definition acid. It perfected the art of using the MSM to scare the wits out of the public. It perfected the art of smearing any scientist with the temerity to question the model assumptions (ex Ed Krug)
Unlike climate change the government’s own report (NAPAP) said the damages associated with acid rain were overblown. Because of the reports conclusion that acid rain was not a crisis- EPA refused to allow the report to be released until AFTER Congress voted on the legislation. (And good luck finding a copy of the final NAPAP report on-line) Science was not a consideration by either EPA or Congress then and it is not a consideration now. I’m unsure how we hope to have science adjudicate climate science when it died during acid rain.
We are now 20 years down the road from the acid rain crisis and there has been no material improvement in surface water pH as promised by the models. And there has been few voices heard asking EPA why the acid models failed so miserably yet climate models are to be believed implicitly.
Most the causation/ correlation links made to support the acid rain models are now being used to support the climate change models. Forests are now dead because of insect infestation caused by climate change– the same forests that 20 years ago were wilting from acid rain. Atlantic salmon are declining because of elevated temperature and twenty years ago from acidity. Surface water pH has failed to improve despite SO2 controls because increased temperatures stimulating the production of excess organic acids– the same natural organic acids that Ed Krug was smeared for saying created the natural acid conditions of most acidic waters in the US. Academic chemists that blamed everything on acid rain now get to blame the same things on climate change- talk about your renewable resource.
Climate change is simply the most recent incarnation of a very corrupt system. A system that in the near term seems to be impervious to science.
Slartibartfast (11:41:36) :
Not fixed! 32.5 degrees North latitude runs through central Texas; 32.5 degrees South latitude runs through Uruguay.
Texas and Uruguay don’t share any longitudes. Uruguay is entirely (hundreds of miles) east of any point in the United States.
————-
Quite true.
The original NASA news release should have said:
The new analysis shows, for example, that at one value of latitude
http://www.nasa.gov/topics/solarsystem/features/uv-exposure.html
Each value of latitude has two circles on the globe (except 0 deg – one, the equator – and 90 deg – two points ). For example, the Tropic of Capricorn and the Tropic of Cancer both have the same latitude values – 23º 26′ 17″.
It looks like the UV effect is basically symmetrical about the equator, until you start getting to high latitude southern values, and encounter the ozone hole over Antarctica.
Anyway, regulating human activities because they are affecting the global atmosphere – that’s just crazy talk. Humans have no effect whatsoever on the global atmosphere.
Leif Svalgaard (10:09:12) :
Leif Svalgaard (08:27:43) :
Leif Svalgaard (08:26:59) :
The largest increases in UV (shown in white, red, orange, and yellow) have occurred in the southern hemisphere during summers.
During winters….
It’s from NASA Dr Svalgaard.
“From NASA Goddard press release here”
Why would you expect anything to be correct (Mars lander anyone? Hubble..)?
A simple question.
How do we know the ‘ozone hole’ wasn’t there before we detected it? Or that it was there always?
OT: An Atlantic El Nino?
http://www.osdpd.noaa.gov/data/sst/anomaly/anomnight.current.gif
Enneagram (14:42:45) :
“OT: An Atlantic El Nino?
http://www.osdpd.noaa.gov/data/sst/anomaly/anomnight.current.gif”
Somewhat different result here
http://weather.unisys.com/surface/sst_anom.gif