Next two years hottest, says Met Office 9/15
http://www.bbc.com/news/science-environment-34226178
The next two years could be the hottest on record globally, says research from the UK's Met Office.
It warns big changes could be under way in the climate system with greenhouse gases increasing the impact of natural trends. The research shows that a major El Nino event is in play in the Pacific, which is expected to heat the world overall. But it also reveals that summers in Europe might get cooler for a while as the rest of the globe warms.
The scientists confirm that in 2015 the Earth's average surface temperature is running at, or near, record levels (0.68C above the 1961-1990 average).
Volcanic caveat
Met Office Hadley Centre director Prof Stephen Belcher said: "We know natural patterns contribute to global temperatures in any given year, but the very warm temperatures so far this year indicate the continued impact of (manmade) greenhouse gases. "With the potential that next year could be similarly warm, it's clear that our climate continues to change."
An external reviewer, Prof Rowan Sutton, from the University of Reading, confirmed: "Unless there's a big volcanic eruption, it looks very likely that globally 2014, 2015 and 2016 will be among the very warmest years ever recorded." "This isn't a fluke. We are seeing the effects of energy steadily accumulating in the Earth's oceans and atmosphere, caused by greenhouse gases."
California reprieve?
The scientists say that the combination of the effect of increasing CO2, coupled with long-term natural ocean trends, leaves the climate system looking "very interesting". They suspect major changes may be under way. Prof Adam Scaife from the Met Office said: "It's an important turning point in the Earth's climate with so many big changes happening at once."
Two trends affecting weather patterns in the near and medium term are in the Pacific Ocean. El Nino happens when a Pacific current reverses on average every five years or so, bringing downpours where there is normally drought and drought where there is normally rain. El Nino tends to push world temperatures upwards.
This growing event is now looking similar to the 1998 El Nino, which bleached corals and brought havoc to world weather systems. The current event could increase drought risk in South Africa, East Asia, and the Philippines - and bring floods to southern South America. One good outcome might be the end of the crippling, four-year California drought.
Arctic implication
The second natural change is a shift in the decadal temperature pattern in the North Pacific known as the PDO. It has been in a cool phase, which the Met Office says has contributed to the pause in the rise of average surface atmospheric temperatures over the past decade. Now, it is entering a warm phase, which will typically make the world hotter.
But there's another factor at play. These two warming events will be partly offset by the North Atlantic temperature pattern (AMO) switching into a cool phase. The scientists say they have recently learned more about how these great ocean patterns temper or accelerate human-induced warming, but Prof Sutton said: "The bit we don't understand is the competition between those factors - that's what we are working on."
So the researchers can say that changes in the Atlantic mean Europe is likely to get slightly cooler and drier summers for a decade - but only if the Atlantic signal is not overridden by the Pacific signal. And they cannot be sure yet which influence will prevail.
The Atlantic cooling could lead to the recovery of sea-ice in adjacent Arctic areas.
Energy input
The Met Office is being ultra-cautious after being castigated for what some said were over-confident decadal forecasts in the past, when natural ocean trends were less well understood.
When asked when the pause in surface warming would end, they stressed that from their perspective there was no real pause in the Earth's warming because the oceans continued to heat, sea levels continued to rise and ice continued to melt.
Prof Scaife said: "We can't be sure this is the end of the slowdown, but decadal warming rates are likely to reach late 20th-Century levels within two years."
And Prof Sutton warned: "If greenhouse gas-driven warming continues unabated, the long-term effects on global and regional climate will dwarf those of short-term fluctuations like El Nino."
未來兩年 歷來最熱
英國氣象局指出，未來兩年可能是全球歷來最高溫的時候。
隨著溫室氣體的增加，氣候系統的自然調節機制將受到極大的改變。研究顯示，太平洋目前正發生較強烈的聖嬰現象，預期會提高全球的溫度。但這也表示，在其他地區變暖的同時，歐洲夏季可能有一段時間會較為涼爽。
科學家證實，2015年地表平均溫度將會迅速到達──或逼近──歷來最高溫記錄，比1961到1990的平均溫度高出攝氏0.68度。
警惕火山活動
英國氣象局哈德利中心(Met Office Hadley Centre)主任Stephen Belche教授表示：「我們知道，在任何一年裡全球氣溫都有其自然循環，但由目前達到的極暖溫度看來，人類持續排放的溫室氣體是暖化的元兇。」「明年很可能也一樣炎熱，這顯示了氣候正在不斷地改變。
外部審稿人──雷丁大學(University of Reading)教授Rowan Sutton也證實：「除非有大規模的火山爆發減緩暖化速度，否則2014到2016年將很可能成為歷來記錄中最熱的幾年。」「這並非偶然，我們可以看到溫室氣體不斷累積在海洋及大氣所帶來的影響。」
加州解渴？
科學家認為，不斷增加的二氧化碳加上長期洋流的影響，使得全球氣候系統處於非常特別的狀態，他們懷疑有極大的改變正在醞釀。英國氣象局Adam Scaife教授表示：「同時發生的這些許多大改變，將是全球氣候的一個重大轉捩點」。
影響近期氣候的因素有兩大方向，一是聖嬰現象，二是太平洋年代震盪(Pacific Decadal Oscilaltion,PDO)。
聖嬰現象平均約每五年會發生一次，太平洋洋流轉向使得平常乾燥的地區降下豪雨，有雨的地方則造成乾旱。當前不斷增強的聖嬰現象與1998年造成珊瑚白化與氣候系統異常的情況相似，將推升全球氣溫，可能導致南非、中東與菲律賓的乾旱危機，並在南美洲南部帶來洪水。唯一樂觀的結果是，美國加州四年來的乾旱可望結束。
牽涉北極地區情況
而太平洋年代震盪則會影響十年左右的氣候模式。英國氣象局表示，原本處於涼爽期、暫緩平均地表氣溫上升的模式現已進入溫暖期，這將使得全球氣溫升高。但還有另一個因素要納入考慮，這兩個影響氣溫上升的活動也會部分被大西洋多年代振盪（Atlantic Multidecadal Oscillation, AMO）的涼爽期所抵銷。
雖然近來科學家已經逐漸了解海洋如何緩解或加速人為的暖化現象，「但我們並不了解這些因素之間的角力，所以我們現在正致力於研究這個部分。」Sutton教授說道。究竟哪一鼓力量會佔上風目前並無法預知，科學家只知道當太平洋的力量壓過北極地區時，歐洲夏季才可能有十年的時間較為涼爽乾燥。
投入更多研究
由於過往對洋流的了解並不充份，在被譴責過去對十年來的氣候預測過度自信後，英國氣象局現已十分小心，當被問到暖化放緩的週期何時會結束時，他們強調：因為海洋持續加溫，冰山溶解、海平面不斷上升，事實上暖化現象並沒有真正的暫緩階段存在。
Scaife教授表示：「我們無法確知暖化放緩的週期何時結束，但在未來兩年，很可能達到20世紀後期十年來的升溫速度。」Sutton教授也警告：「如果溫室氣體造成的暖化現象並未減退的話，長期看來，全球氣候變化受到像是聖嬰現象等短期波動的影響將會減少。」
