Neue Nature-Studie: US-Wetter hat sich in den letzten 40 Jahren deutlich verbessert. Winter wärmer, Sommer gleichbleibend

Endlich einmal gute Klimanachrichten. Die österreichische Tageszeitung Die Presse meldete am 20. April 2016:

Die Erwärmung tut in Amerika vielen wohl

Die Warnungen vor katastrophalen Folgen finden in den USA deshalb so wenig Gehör, weil sie schlecht zur Erfahrung passen: Fast im gesamten Land ist das Wetter in den vergangenen 40 Jahren besser geworden.

Wenn man die Elche fragen könnte, was sie vom Klimawandel halten, wäre die Antwort klar: Zwar hat der UNO-Klimabeirat IPCC 2007 prognostiziert, „40 bis 70 Prozent“ der Arten würden durch die Erwärmung verschwinden. Aber bisher ist davon nichts zu sehen, nicht eine Art ist ausgestorben. Im Gegenteil, viele haben davon profitiert, dass sie ihre Lebensräume ausweiten konnten. Etwa die Schmetterlinge: Ihre britischen Freunde von der Butterfly Conservation freuten sich in ihrer Jahresbilanz 2011 darüber, dass der Admiral (Vanessa atalante) nicht länger nur Sommergast auf der Insel ist, sondern auch im Winter dort bleibt.

Nun kommen zu den Klimagewinnern die Elche hinzu, überall dringen sie aus den Wäldern des Nordens noch weiter nach Norden vor, in die Tundren. Für Alaska hat Ken Tape (University of Alaska) es dokumentiert: In den dortigen Tundren gab es sie im frühen 20. Jahrhundert kaum, inzwischen sind sie Hunderte Kilometer vorgewandert, weiter geht oft nicht, sie sind schon an den Küsten.

Weiterlesen in Die Presse

Der Knackpunkt: In einer am 20. April 2016 in Nature erschienenen Studie konnten Patrick Egan und Megan Mullin zeigen, dass sich das Wetter in den USA zwischen 1974-2013 insgesamt verbessert hat. Die Winter sind milder geworden, während sich im Sommer im Prinzip nichts änderte. Hier der erste Teil der Kurzfassung:

Recent improvement and projected worsening of weather in the United States
As climate change unfolds, weather systems in the United States have been shifting in patterns that vary across regions and seasons1, 2, 3, 4, 5, 6, 7. Climate science research typically assesses these changes by examining individual weather indicators, such as temperature or precipitation, in isolation, and averaging their values across the spatial surface. As a result, little is known about population exposure to changes in weather and how people experience and evaluate these changes considered together. Here we show that in the United States from 1974 to 2013, the weather conditions experienced by the vast majority of the population improved. Using previous research on how weather affects local population growth8, 9, 10, 11, 12, 13, 14 to develop an index of people’s weather preferences, we find that 80% of Americans live in counties that are experiencing more pleasant weather than they did four decades ago. Virtually all Americans are now experiencing the much milder winters that they typically prefer, and these mild winters have not been offset by markedly more uncomfortable summers or other negative changes.

Ein schönes Ergebnis. Nun hätte Nature diese Studie vermutlich nicht zum Druck angenommen, wenn die Autoren nicht noch kräftig Klimalarm hineingerührt hätten. Mithilfe unkalibrierter Klimamodelle spekulieren die Autoren, dass es in Zukunft jetzt alles viel schlechter wird. Und weil die doofen Amerikaner das noch nicht wissen, wären sie überwiegend Klimaleugner. Zwei tolle Pointen. Ein schönes Beispiel für rhetorischen Unsinn, mit dem heute seriöse Forschung angefettet werden muss, um nicht in den Verdacht klimaskpetischer Tendenzen zu geraten.

Die New York University gab am 20. April 2016 die folgende Pressemitteilung zur Studie heraus, die von den meisten deutschsprachigen Zeitungen ignoriert wurde:

Recent warmer winters may be cooling climate change concern

The vast majority of Americans have experienced more favorable weather conditions over the past 40 years, researchers from New York University and Duke University have found. The trend is projected to reverse over the course of the coming century, but that shift may come too late to spur demands for policy responses to address climate change.

The analysis, published in the journal Nature, found that 80 percent of Americans live in counties where the weather is more pleasant than four decades ago. Winter temperatures have risen substantially throughout the United States since the 1970s, but summers have not become markedly more uncomfortable. The result is that weather has shifted toward a temperate year-round climate that Americans have been demonstrated to prefer.

“Rising temperatures are ominous symptoms of global climate change, but Americans are experiencing them at times of the year when warmer days are welcomed,” explains Patrick J. Egan, an associate professor in NYU’s Wilf Family Department of Politics who authored the study with Duke’s Megan Mullin.

However, he and Mullin, an associate professor at Duke’s Nicholas School of the Environment, discovered a looming shift in these patterns when they used long-term projections of temperature changes to evaluate future weather Americans are likely to experience. According to these estimates, nearly 90 percent of the U.S. public may experience weather at the end of the 21st century that is less preferable than weather in the recent past.

“Weather patterns in recent decades have been a poor source of motivation for Americans to demand policies to combat the climate change problem,” observes Mullin. “But without serious efforts to reduce greenhouse gas emissions, year-round climates ultimately will become much less pleasant.”

In a 2012 study, the duo found that local weather temporarily influences people’s beliefs about evidence for global warming. That research, which appeared in the Journal of Politics, found that those living in places experiencing warmer-than-normal temperatures at the time they were surveyed were significantly more likely than others to say there is evidence for global warming.

In the Nature study, Egan and Mullin took a broader approach to understanding weather patterns–and how Americans experience them. The researchers analyzed 40 years of daily weather data (from 1974 through 2013) on a county-by-county basis to evaluate how the population’s experience with weather changed during this period, which is when climate change first emerged as a public issue.

They found that Americans on average have experienced a steep rise in January maximum temperatures–an increase of 1.04 °F per decade (0.58 °C). By contrast, daily maximum temperatures in July rose by only 0.13 °F per decade (0.07 °C). Moreover, humidity in the summer has declined somewhat since the mid-1990s. In other words, winter temperatures have become warmer for virtually all Americans while summer conditions have remained relatively constant.

To quantify how Americans are evaluating these changes, Egan and Mullin drew upon research by economists examining weather’s role in growth of the Sun Belt and population declines in the Northeast and Midwest. Using these findings, they developed a metric of the average American’s preferences about weather. This “weather preference index” (WPI) reflects the U.S. public’s preferences for places with warmer temperatures in winter and cooler temperatures and lower humidity in summer. The index also takes into account preferences about precipitation. Egan and Mullin found that WPI scores have risen in counties accounting for 80 percent of the U.S. population since the 1970s.

But projections of future temperatures–and future WPI scores–offer a markedly different picture. Climate change models predict that under all potential levels of future warming, average summer temperatures will ultimately rise at a faster rate than winter temperatures. Using these projections, the researchers calculated that under a severe warming scenario, WPI scores will decline such that an estimated 88 percent of the U.S. public will experience less pleasant weather at the end of this century than it has in the past 40 years.