Kehrtwende in der Konfliktforschung: Nicht steigende Temperaturen, sondern geringe saisonale Unterschiede fördern Aggression

Ein Labor zur organischen Geochemie des Geologischen Dienstes der USA (USGS) wurde am 1. März 2016 geschlossen, nachdem bekannt wurde, dass dort fast zwanzig Jahr lang Daten manipuliert wurden. Projekten im Wert von insgesamt 108 Millionen US$ wurde damit die Datengrundlage entzogen. Etliche Publikationen mussten zurückgezogen werden. Der Folgeschaden durch Zitate falscher Ergebnisse ist noch unbekannt. Ob auch Projekte zum Klimawandel betroffen sind? Der USGS leitete ein Disziplinarverfahren ein, allerdings weigerte sich der Geologische Dienst, den Namen des manipulierenden Mitarbeiters bekanntzugeben.

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Vor drei Jahren hatten Forscher die Idee, dass der Klimwandel zu mehr Aggression in der Welt führen würde, weil Menschen mit steigenden Temperaturen aggressiver wären. Die Welt berichtete am 1.8.2013:

Steigende Temperaturen machen uns aggressiv
Hitze tut den Menschen nicht gut. Immer, wenn es warm war, bekriegten sich die Menschen – das beweist der Rückblick auf die vergangenen 10.000 Jahre. Es gibt jedoch auch Zweifel an dieser These.
Das Klima beeinflusst das Gewaltverhalten der Menschen. Selbst eine geringe Abweichung von der üblichen Temperatur oder Regenmenge erhöhe das Risiko von Konflikten, berichten US-Forscher im Fachblatt “Science”. Dies gelte rund um die Welt und zwar sowohl für die heutige Zeit als auch schon in der Vergangenheit. [...] Vor allem höhere Temperaturen führten demnach zu einer Zunahme der Gewalt. Eine Standardabweichung von der Temperatur – das entspricht zum Beispiel einer Temperaturerhöhung von 0,4 Grad Celsius über das ganze Jahr in einem afrikanischen Land – hatte zur Folge, dass das Risiko persönlicher Konflikte um vier Prozent stieg. [...] Das Klima sei nicht der einzige und auch nicht der hauptsächliche Grund für den Anstieg der Gewalt. Wenn kommende Generationen ähnlich reagierten wie die vergangenen und derzeit lebenden, könne der Klimawandel allerdings zu erheblich mehr Konflikten rund um die Welt führen.

Mittlerweile ist man sich nicht mehr so sicher, ob das ursprüngliche Modell stimmt. In einer Pressemitteilung vom 24. Juni 2016 meldete die Ohio State University ernsthafte Zweifel am simplistischen Zusammenhang zwischen Temperatur und Aggressionspotential an. Laut einer neuen Studie spielt vielmehr die Ausprägung der Jahreszeiten eine Hauptrolle. In äquatornahen Gebieten treten in der Regel die höchsten Aggressionslevel auf. Dort herrscht über das Jahr hinweg ein recht ähnliches Klima, was zu einer “schnelleren Lebensweise” führt, ohne die gesteigerte Notwendigkeit zur Planung des Lebens. Die lockerere Lebensweise spiegelt sich dann in einem höheren Aggressionspotential wieder. Der Begriff “Klimawandel” (climate change) taucht im gesamten Artikel kein einziges Mal auf und hat im neuen Modell auch nichts zu suchen. Im Folgenden die Pressemitteilung in voller Länge:

How does climate affect violence? Researchers offer new theory: Climate impacts life strategies, time orientation, self-control

Researchers have long struggled to explain why some violent crime rates are higher near the equator than other parts of the world. Now, a team of researchers have developed a model that could help explain why. This new model goes beyond the simple fact that hotter temperatures seem to be linked to more aggressive behavior. The researchers believe that hot climates and less variation in seasonal temperatures leads to a faster life strategy, less focus on the future, and less self-control — all of which contribute to more aggression and violence. “Climate shapes how people live, it affects the culture in ways that we don’t think about in our daily lives,” said Brad Bushman, co-author of the study and professor of communication and psychology at The Ohio State University.

Paul van Lange, lead author of the study and a professor of psychology at the Vrije Universiteit Amsterdam (VU) added, “We believe our model can help explain the impact of climate on rates of violence in different parts of the world.” The researchers, which included Maria I. Rinderu of VU, call the new model CLASH (CLimate Aggression, and Self-control in Humans). They describe the CLASH model in an online article in the journal Behavioral and Brain Sciences.

Many studies have shown that levels of violence and aggression are higher in hot climates, according to the researchers. “But the two leading explanations of why that is so aren’t satisfactory,” Bushman said. The General Aggression Model (which Bushman helped develop) suggests hot temperatures make people uncomfortable and irritated, which makes them more aggressive. “But that doesn’t explain more extreme acts, such as murder,” he said. Another explanation (Routine Activity Theory) is that people are outdoors and interacting more with others when the weather is warm, which leads to more opportunities for conflict. But that doesn’t explain why there’s more violence when the temperature is 95 degrees F (35 °C) than when it is 75 degrees F (24 °C) — even though people might be outside under both circumstances.

The CLASH model states that it is not just hotter temperatures that lead to more violence — it is also climates that have less seasonal variation in temperature. “Less variation in temperature, combined with heat, brings some measure of consistency to daily life,” Rinderu said. That means there is less need to plan for large swings between warm and cold weather. The result is a faster life strategy that isn’t as concerned about the future and leads to less need for self-control. “Strong seasonal variation in temperature affects culture in powerful ways. Planning in agriculture, hoarding, or simply preparing for cold winters shapes the culture in many ways, often with people not even noticing it. But it does shape how much a culture values time and self-control,” Van Lange said. “If there is less variation, you’re freer to do what you want now, because you’re not preparing foods or chopping firewood or making winter clothes to get you through the winter. You also may be more concerned with the immediate stress that comes along with parasites and other risks of hot climates, such as venomous animals.”

People living in these climates are oriented to the present rather than the future and have a fast life strategy — they do things now. “We see evidence of a faster life strategy in hotter climates with less temperature variation — they are less strict about time, they have less use of birth control, they have children earlier and more often,” Bushman said. With a faster life strategy and an orientation toward the present, people have to practice less self-control, he said. That can lead people to react more quickly with aggression and sometimes violence.

The theory is not deterministic and isn’t meant to suggest that people in hotter, consistent climates can’t help themselves when it comes to violence and aggression. “How people approach life is a part of culture and culture is strongly affected by climate,” Van Lange said. “Climate doesn’t make a person, but it is one part of what influences each of us. We believe it shapes the culture in important ways,” he said.

Since CLASH is a new theory, studies have to be done to prove it is correct. But Bushman said a lot of evidence already suggests that the theory may be on to something. “We believe CLASH can help account for differences in aggression and violence both within and between countries around the world,” he said. “We think it provides a strong framework for understanding the violence differences we see around the world.”

 

Paper:
Paul A. M. Van Lange, Maria I. Rinderu, and Brad J. Bushman. Aggression and Violence Around the World: A Model of CLimate, Aggression, and Self-control in Humans (CLASH). Behavioral and Brain Sciences, June 2016