Summary: SUMMARY: This week on Radio Ecoshock 3 interviews with scientists on the cutting edge of climate change. From the UK, Chris Boulton hunts for signs of abrupt ecological shifts. From Norway, Hans Weihe explores the changing Arctic. But first, we look into whether air pollution is shading the world from serious heating, with Bjorn Stevens of the Max Planck Institute in Germany. Download or listen to this Radio Ecoshock show in CD Quality (56 MB) or Lo-Fi (14 MB) Or listen on Soundcloud right now! IS IT SAFE TO CLEAN UP AIR POLLUTION? DR. BJORN STEVENS We know that industrial pollution in the atmosphere actually hides some of the global warming expected from our emissions. But how much? Respected scientists like James Hansen have suggested that a degree Celsius - or more - is "in the pipeline" due to the pollution, called "aerosols" in science. The Intergovernmental Panel on Climate Change has a wide range of possible impacts of aerosols, but they recently dropped their lowest estimates. The whole subject is one of the most difficult in science, because it involves swirls of widely varying materials in the atmosphere, unevenly distributed around the globe. The aerosols also interact with one of the last frontiers of science, the activity of clouds. Our guest Professor Bjorn Stevens is a director at the Max-Planck-Institute for Meteorology where he leads the Atmosphere in the Earth System Department. He is also a professor at the University of Hamburg. Dr. Stevens was previously at the University of California in Los Angeles. Although born in Germany, he is an American, educated in the United States. Bjorn Stevens is one of the world authorities on clouds and climate change. He's the lead author of a new paper on the limits of aerosol impacts on global warming - and that paper has already stirred up controversy, including among climate sceptics. The public knows little about this scientific discussion, except when it's called "global dimming". I've run a feature about it by the BBC. I was also impressed by studies of what was first called the "Asian Brown Cloud", but later the "Atmospheric Brown Cloud". Below you will find a link to my 2006 program on the subject, featuring the work of V. Ramanathan of the Scripps Institute. For example, simple studies of how long it takes a pan of water to evaporate showed sunlight reaching the surface of China has dropped by at least 10% over the last couple of decades. Consider the implications for agriculture. Another huge big brown cloud forms over Northern India for part of every year, blocking out sunlight. The cause is mostly soot from inefficient indoor cooking fires! In that blog I wrote: "Ramanathan told science writer Regina Nuzzo, 'By sheer, dumb luck, we are adding particles that are trapping sunlight and cooling the planet.' He compares it to a mask - and if that pollution is removed, the climate may suddenly rise to the real levels of warming gases in the atmosphere. Ramanathan said: 'Many of us, including myself, are concerned we could see a huge acceleration of global warming if we unmask the beast.'" GLOBAL DIMMING RESOURCES: Find a text summaryof the BBC "Global Dimming" documentary here. Watch the documentary here. The Radio Ecoshock special on global dimming (20 minutes, 18 MB) is available as a free .mp3 here. A transcript of Radio Ecoshock special on global dimming, (broadcast Sept 8, 2006) is here. BUT IS GLOBAL DIMMING AN IMPORTANT PROBLEM NOW? But now in 2015 we ask: is global dimming an appropriate label for the totality of human pollution that may be shading the Earth from the real carbon blanket we've put up there? If I understood him correctly, Bjorn Stevens says "no" because global dimming was really about local or regional conditions of pollution (say over India or China) rather than a global effect. In fact, Stevens began to argue with other scientists who claimed a large amount of warming was being masked. That argument became his new paper "Rethinking the Lower
