Fwd: [EANTH-L] NY Times essay on climate change science

[Henk Vreekamp]

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Commentaar van milieuspecialist in NYTimes:

>>NY Times
>>February 6, 2007
>>Essay
>>
>>
>>
>>On the Climate Change Beat, Doubt Gives Way to Certainty
>>
>>
>>
>>
>>
>>By 
>><http://topics.nytimes.com/top/reference/timestopics/people/s/william_k_stevens/index.html?inline=nyt-per>WILLIAM 
>>K. STEVENS
>>
>>In the decade when I was the lead reporter on 
>><http://topics.nytimes.com/top/news/science/topics/globalwarming/index.html?inline=nyt-classifier>climate 
>>change for this newspaper, nearly every blizzard or cold wave that hit 
>>the Northeast would bring the same conversation at work.
>>
>>Somebody in the newsroom would eye me and say something like, “So much 
>>for global warming.” This would often, but not always, be accompanied by 
>>teasing or malicious expressions, and depending on my mood the person 
>>would get either a joking or snappish or explanatory response. Such an 
>>exchange might still happen, but now it seems quaint. It would be out of 
>>date in light of a potentially historic sea change that appears to have 
>>taken place in the state and the status of the global warming issue since 
>>I retired from The New York Times in 2000.
>>
>>Back then I wrote that one day, if mainstream scientists were right about 
>>what was going on with the earth’s climate, it would become so obvious 
>>that human activity was responsible for a continuing rise in average 
>>global temperature that no other explanation would be plausible.
>>
>>That day may have arrived.
>>
>>Similarly, it was said in the 1990s that while the available evidence of 
>>a serious human impact on the earth’s climate might be preponderant 
>>enough to meet the legal test for liability in a civil suit, it fell 
>>short of the more stringent “beyond a reasonable doubt” test of guilt in 
>>a criminal case.
>>
>>Now it seems that the steadily strengthening body of evidence about the 
>>human connection with global warming is at least approaching the higher 
>>standard and may already have satisfied it.
>>
>>The second element of the sea change, if such it is, consists of a 
>>demonstrably heightened awareness and concern among Americans about 
>>global warming. The awakening has been energized largely by dramatic 
>>reports on the melting Arctic and by fear ­ generated by the spectacular 
>>horror of Hurricane Katrina ­ that a warmer ocean is making 
>><http://topics.nytimes.com/top/reference/timestopics/subjects/h/hurricanes_and_tropical_storms/index.html?inline=nyt-classifier>hurricanes 
>>more intense.
>>
>>Politicians are weighing in on the subject as never before, especially 
>>with the advent of a Democratic-led Congress. It appears likely, if not 
>>certain, that whoever is elected president in 2008 will treat the issue 
>>seriously and act accordingly, thereby bringing the United States into 
>>concert with most of the rest of the world. Just last week, Senator 
>><http://topics.nytimes.com/top/reference/timestopics/people/m/john_mccain/index.html?inline=nyt-per>John 
>>McCain of Arizona, a presidential aspirant and the co-author of a bill 
>>mandating stronger action, asserted that the argument about global 
>>warming “is over.” Back in the day, such words from a conservative 
>>Republican would have been unimaginable, even if he were something of a 
>>maverick.
>>
>>I’ve been avidly watching from the sideline as the strengthening evidence 
>>of climate change has accumulated, not least the discovery that the 
>>Greenland ice cap is melting faster than had been thought. The 
>>implications of that are enormous, though the speed with which the 
>>melting may catastrophically raise sea levels is uncertain ­ as are many 
>>aspects of what a still hazily discerned climatic future may hold.
>>
>>Last week, in its first major report since 2001, the world’s most 
>>authoritative group of climate scientists issued its strongest statement 
>>yet on the relationship between global warming and human activity. The 
>>Intergovernmental Panel on Climate Change said the likelihood was 90 
>>percent to 99 percent that emissions of heat-trapping greenhouse gases 
>>like carbon dioxide, spewed from tailpipes and smokestacks, were the 
>>dominant cause of the observed warming of the last 50 years. In the 
>>panel’s parlance, this level of certainty is labeled “very likely.”
>>
>>Only rarely does scientific odds-making provide a more definite answer 
>>than that, at least in this branch of science, and it describes the 
>>endpoint, so far, of a progression:
>>
>>¶In 1990, in its first report, the panel found evidence of global warming 
>>but said its cause could be natural as easily as human.
>>
>>¶In a landmark 1995 report, the panel altered its judgment, saying that 
>>“the balance of evidence suggests a discernible human influence on global 
>>climate.”
>>
>>¶In 2001, it placed the probability that human activity caused most of 
>>the warming of the previous half century at 66 percent to 90 percent ­ a 
>>“likely” rating.
>>
>>And now it has supplied an even higher, more compelling seal of numerical 
>>certainty , which is also one measure of global warming’s risk to humanity.
>>
>>To say that reasonable doubt is vanishing does not mean there is no doubt 
>>at all. Many gaps remain in knowledge about the climate system. 
>>Scientists do make mistakes, and in any case science continually evolves 
>>and changes. That is why the panel’s findings, synthesized from a vast 
>>body of scientific studies, are generally couched in terms of 
>>probabilities and sometimes substantial margins of error. So in the 
>>recesses of the mind, there remains a little worm of caution that says 
>>all may not be as it seems, or that the situation may somehow 
>>miraculously turn around ­ or, for that matter, that it may turn out 
>>worse than projected.
>>
>>In several respects, the panel’s conclusions have gotten progressively 
>>stronger in one direction over almost two decades, even as many of its 
>>hundreds of key members have left the group and new ones have joined. 
>>Many if not most of the major objections of contrarians have evaporated 
>>as science works its will, although the contrarians still make themselves 
>>heard.
>>
>>The panel said last week that the fact of global warming itself could now 
>>be considered “unequivocal,” and certified that 11 of the last 12 years 
>>were among the 12 warmest on record worldwide. (The fact of the warming 
>>is one thing contrarians no longer deny.)
>>
>>But perhaps the most striking aspect of the 2007 report is the sheer 
>>number and variety of directly observed ways in which global warming is 
>>already having a “likely” or “very likely” impact on the earth.
>>
>>In temperate zones, the frequency of cold days, cold nights and frosts 
>>has diminished, while the frequency of hot days, hot nights and heat 
>>waves has increased. Droughts in some parts of the world have become 
>>longer and more intense. Precipitation has decreased over the subtropics 
>>and most of the tropics, but increased elsewhere in the Northern and 
>>Southern Hemispheres.
>>
>>There have been widespread increases in the frequency of “heavy 
>>precipitation events,” even in areas where overall precipitation has gone 
>>down. What this means is that in many places, it rains and snows less 
>>often but harder ­ well-documented characteristics of a warming 
>>atmosphere. Remember this in the future, when the news media report 
>>heavy, sometimes catastrophic one-day rainfalls ­ four, six, eight inches 
>>­ as has often happened in the United States in recent years. Each one is 
>>a data point in an trend toward more extreme downpours and the floods 
>>that result.
>>
>>All of these trends are rated 90 percent to 99 percent likely to continue.
>>
>>The list goes on.
>>
>>And for the first time, in the wake of Hurricane Katrina, the panel 
>>reported evidence of a trend toward more intense hurricanes since 1970, 
>>and said it was likely that this trend, too, would continue.
>>
>>Some of the panel’s main conclusions have remained fairly stable over the 
>>years. One is that if greenhouse gas emissions continue unabated, they 
>>will most likely warm the earth by about 3 to 7 degrees Fahrenheit by the 
>>end of this century, with a wider range of about 2 to 12 degrees 
>>possible. The warming over the Northern Hemisphere is projected to be 
>>higher than the global average, as is the case for the modest one-degree 
>>warming observed in the last century.
>>
>>The projected warming is about the same as what the panel estimates would 
>>be produced by a doubling of atmospheric concentrations of greenhouse 
>>gases, compared with the immediate preindustrial age. It would also be 
>>almost as much warming as has occurred since the depths of the last ice 
>>age, 20,000 years ago.
>>
>>Some experts believe that no matter what humans do to try to rein in 
>>greenhouse gas emissions, a doubling is all but inevitable by 2100. In 
>>this view, the urgent task ahead is to keep them from rising even higher.
>>
>>If the concentrations were to triple, and even if they just double, there 
>>is no telling at this point what the world will really be like as a 
>>result, except to speculate that on balance, most of its inhabitants 
>>probably won’t like it much. If James E. Hansen, one of the bolder 
>>climate scientists of the last two decades, is right, they will be living 
>>on a different planet.
>>
>>It has been pointed out many times, including by me, that we are engaged 
>>in a titanic global experiment. The further it proceeds, the clearer the 
>>picture should become. At age 71, I’m unlikely to be around when it 
>>resolves to everyone’s satisfaction ­ or dissatisfaction. Many of you may 
>>be, and a lot of your descendants undoubtedly will be.
>>
>>Good luck to you and to them.

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