Air Date: Week of April 21, 2006

Dr. Martin Wild prepares for a climate conference in Vienna, Austria. (Dr. Martin Wild)

Recent research shows that the amount of sunlight getting through the Earth’s atmosphere has dropped since 1945. But as our skies got cleaner during the 90's, sunlight levels bounced back. Martin Wild of the Institute for Atmospheric and Climate Science in Zurich, Switzerland tells host Steve Curwood why this phenomenon may speed the warming of the planet due to climate change.

Transcript

CURWOOD: It’s Living on Earth. I’m Steve Curwood. Summer’s coming – a time for hot cars. But I’m not talking about Ferraris or Corvettes. No, I’m talking about the kind of hot you get when the sun beats down on a parked car with the windows rolled up. A reflecting cardboard in the windshield can keep a car cool, and that fact is now telling us something about global warming.

All those aerosols and pollutants we threw into the air in the decades following World War II acted like a shade for the whole planet. Scientists even have a name for this phenomenon. They call it “Solar Dimming,” and they say it has shielded us from the full impact of global warming. But now they say the shade is disappearing.

Joining me is Dr. Martin Wild of the Institute for Atmospheric and Climate Science in Zurich, Switzerland. Hello, sir.

WILD: Hello.

CURWOOD: Dr. Wild, it seems that the amount of sunlight that gets through to Earth varies in different places around the world.

WILD: That’s true. That’s true. We found that particularly during the 60s up to the 80s there have been many parts of the globe the sunlight has become less and less. And at our institute in Switzerland we collect all the data on available sunshine at the surface, and what we see in this data is that there has been dimming of a large part of the globe. And this dimming was particularly pronounced between the 1960s and 1980s. And we believe that the growing air pollution has been an important cause of these changes because the manmade air pollution releases more and more tiny particles into the atmosphere, and these particles can then absorb or scatter back sunlight, and thereby effectively shield the surface from obtaining sunlight

CURWOOD: Now this dimming, you say, was going on from the 60s to the 80s, but seems to be brightening a bit now. Why is that?

WILD: This is due to the fact that the atmosphere has become cleaner, and therefore more transparent, over large parts of the globe during the 1990s. And contributing to this was, on the one hand, the breakdown of the former Communist countries in Russia and Eastern Europe, which resulted in less air pollution. And also air quality measures have become effective in recent years, which helps the atmosphere to become cleaner, and therefore more transparent for sunlight.

CURWOOD: Now how do you measure the amount of sunlight that gets through the atmosphere?

WILD: We have a global network of surface measurements which are set up over wide areas of the globe, and we collect this data to see how sunlight varies over time. And this data made it also possible that we could discover this phenomenon of the global dimming, which is the reduction of sunlight at the Earth’s surface, but also the more recent recovery toward brightening over many pats of the globe.

CURWOOD: How much sunlight was being lost in those decades?

WILD: At the measurements center we can observe the changes that the Earth’s surface received sunlight decreases by about two percent per decade. So this is quite a substantial amount. Now we do not see this continuation of dimming anymore except for some parts of the world which have still-increasing air pollution. One of these examples is the Indian subcontinent. There air pollution is still increasing, and this results in the so-called Asian brown clouds which resides over India, particularly in the dry season, and shields the surface from sunlight.

CURWOOD: So we’re still dimmer today than we were almost 50 years ago, but we’re brighter than we were when things were really polluted?

WILD: That’s true, that’s true, that’s true. That at least applies for the extra tropics. In the tropics in India there is still a tendency that we are now at the lowest level of sunlight which we did not reach before.

CURWOOD: Now how much has the solar dimming masked global warming?

WILD: Well solar dimming has been masking global warming very effectively after the mid-80s. Since then, when dimming disappeared and no longer compensated for the global warming, we see the full dimension of the greenhouse effect. We see this, for example, in an unparalleled temperature rise during the last two decades. As another example, we can mention the mountain glaciers which are retreating very strongly since the mid-80s while the same glaciers did not change at all during the previous decades where dimming still prevented the glaciers from melting away.

CURWOOD: Now some people listening to us might say, Oh, well maybe we should bring the pollution back to help save the Earth from global warming. What would you say to them?

WILD: Yeah, I think we should avoid playing one environmental risk off another one. So both global dimming and warming are issues which we have to take very seriously. Global dimming and its related increase in air pollution causes serious health problems, while global warming, on the other hand, puts severe stress on our ecosystems and worsens our living conditions.

I think it would be therefore disastrous to believe we can fight global warming by global dimming, and by increasing air pollution. I rather believe that in such a complex system like the global ecosystem we can not just try to remedy one problem in isolation. We have to take an integral approach to keep our planet livable. This means we have to reduce as much as possible both air pollution and the release of greenhouse gasses into the atmosphere.

CURWOOD: Switzerland is famous for its alpine skiing. How much has the effect of climate change affected your skiing industry right there in Switzerland?

WILD: I think it’s quite a big problem, so the ski season has become less extended. And also the glaciers have retreated so much everybody can see, and this is of course also, in terms of tourism, a problem because the glaciers are just not there anymore where you could see them a couple of decades before.

CURWOOD: Dr. Martin Wild is with the Institute for Atmospheric and Climate Science in Zurich, Switzerland. Thank you, sir.

WILD: It was my pleasure. Thank you.

 

Links

The Institute for Atmospheric and Climate Science in Zurich, Switzerland.