|
北极海冰的消融，会引发加州森林野火吗？
变暖的气候，消融的海冰与饥饿的北极熊 图片来源：Andreas Weith, CC BY-SA 4.0, via Wikimedia Commons 油与水，苹果与橙子，冰与火……这些东西之间看似毫无联系，事实真的如此吗？ “我们发现越来越多有利于火灾发生的天气与夏季北极海冰的减少相关，这进而导致了秋季美国西部野火的增加。”美国西北太平洋国家实验室（Pacific Northwest National Laboratory）的地球科学家王海龙说，“所以我们分析了几十年来对野火、海冰覆盖以及气候条件的观测数据，以确认北极海冰减少与野火风险之间的关系，我们称之为遥相关（teleconnection）。” 王海龙表示冰与火之间存在“遥相关”这个想法并不新鲜，与所谓的“蝴蝶效应”非常相似。1960年气象学家爱德华·劳伦兹（Edward Lorenz）创造出“蝴蝶效应”一词用来解释混沌理论，概括来说就是：如果某地的一只蝴蝶扇动了的翅膀，扰动了足够多的空气，最终可能在另外某处引发一场龙卷风或者其他大规模的大气风暴。 王海龙说：“这个概念当然不是我们发明的，它在大气科学领域存在已久。由于地球系统内的各种联系，尤其是大气中，某一地区的微小改变可以通过大气循环影响到另外的地区。” 海冰减少与野火天气之间的联系以前就建立过，但王海龙表示先前的发现严重依赖数据的统计关系：“比如说，他们可能发现多年来北极海冰在减少，同时发现美国西部的极端天气比如野火在增加。他们只能意识到这其中存在联系，但无法找到机制来解释哪一个是因，哪一个是果。” 所以王海龙和同事在这些已知统计关系的基础上更进了一步，他们将所有数据应用到可预测野火情况的最新气候模型中。“这样，我们就能确定气候系统的响应机制，包括美国西部的火灾天气，以及对北极海冰的其他响应。”王海龙说道。 于是，他们发现了“两个涡旋的故事”。 王海龙解释说：“夏天的时候，海冰大量消融，海洋能够吸收并储存更多来自阳光的热量，北极更少的海冰覆盖，会让……[查看全文] If Sea Ice Melts in the Arctic, Do Trees Burn in California? Emily Schwing: Oil and water. Apples and oranges. Fire and Ice…none of these things really seem like they have much to do with one another…or do they? Hailong Wang: We found that more fire-favorable weather associated with declines in the Arctic sea ice during summer can increase autumn wildfires over the western United States. Schwing: Hailong Wang is an Earth scientist at the Pacific Northwest National Laboratory in Washington state. Wang: So we analyzed a few decades of observations of how wildfire incidents, sea ice cover and weather conditions to identify a relationship between Arctic sea ice decline and the wildfire risks. We called it a teleconnection. Schwing: Wang says this idea of a fire and ice “tele-connection?” … It’s not new. It’s a lot like the so-called “butterfly effect” - a term coined by meteorologist Edward Lorenz in the 1960’s to explain chaos theory. The idea can be summarized like this: if a butterfly flaps its wings in one location, that could displace enough air to cause a tornado or some other large scale atmospheric storm elsewhere. Wang: We certainly didn't invent this concept, but it has been in the atmospheric sciences for a long time. So, because of the connections within the Earth system, especially in the atmosphere, one small change in one region could affect other regions through the atmospheric circulations. Schwing: Connections between declining sea ice and wildfire weather have been made before. Wang says previous findings have relied heavily on statistical relationships. Wang: For example, they found that maybe Arctic sea ice are declining in many years, and they also found the increase in extreme weather like wildfires in the western U.S. Schwing:...but they could not explain the cause and effect. So Wang and colleagues took those known statistical relationships a step further. The team applied them to a state of the art climate model with wildfire prediction capabilities. Wang: In that way, we were able to identify the response of the climate system, including the fire weather over the western U.S. and other responses to the Arctic sea ice. Schwing: What they found is “a tale of two vortices.” Wang: So when the summer sea ice is much reduced, ocean can absorb and store more heat from sunlight. Less sea ice cover over the Arctic will allow...[full transcript] “ Zou, Y., Rasch, P.J., Wang, H. et al. Increasing large wildfires over the western United States linked to diminishing sea ice in the Arctic. Nat Commun 12, 6048 (2021). |
|
|
