There are many units by which to measure the impact of climate change: degrees of increasing temperature, feet of rising sea level, dollars needed to adapt to a warming world. But a group of scientists in California have put forth an intriguing new unit of measurement: kilometers per year.

    Writing in a paper published Wednesday in Nature, scientists describe what they call the velocity of climate change, or more specifically, the speed of Earth's shifting climatic zones. As global temperature rises over the next century, the scientists argue, Earth's habitable climatic zones will start moving too, generally away from the Equator and toward the poles. That means many species of plants and animals will also have to move in order to survive. Whether or not they do will depend on several factors, but two of the most important are how fast a species can adjust its habitat range, and how quickly that range is moving out from under it.

    Until now, ecologists have mostly focused on these factors as they affect individual species, but the new paper takes a more global view. By combining temperature projections on a very fine scale with global topographic maps, researchers have predicted change not for specific species, but for the climatic zones they need to keep up with.

    Indeed, because global temperature is rising now, ecosystems are already on the move. "Once you explain it to people, it makes intuitive sense," says co-author David Ackerly, a University of California, Berkeley, biologist. "We know what it's like to drive north to escape the heat. It's concrete, rather than the abstractness of rising average temperatures."

    More than intuitive, this new index could also prove very useful, especially to conservationists who work to keep species from extinction. While the average velocity of climate change may be a bit less than a half-kilometer per year worldwide, according to the paper, it can be significantly faster or slower depending on the local topography. In deserts and other flat areas, such as the Amazon basin, climatic zones will move faster, while hilly or mountainous terrain will slow things up. "In the Northern Hemisphere, for example," explains lead author Scott Loarie, "north-facing slopes tend to be cooler and wetter than south-facing slopes."

    In short, opposite sides of a mountain may have different climates, even though they're close to each other. In areas with varied terrain including lots of hills, therefore, hospitable conditions might be available relatively nearby. "That was the unexpected message," says Loarie, an ecologist at the Carnegie Institution for Science at Stanford University. "There's lots of buffering capacity in heterogeneous landscapes."

    According to the velocity maps that Loarie and his colleagues put together, only 8% of the world's national parks and other preserves will retain their current climate over the next century, compounding the problem of how to keep species from going extinct. One way to do that is simply to move them. But that's not only extraordinarily difficult, it can also backfire - just ask anyone in the southeastern U.S. about the inexorable advance of the imported invasive species the kudzu vine. "For some species on the brink of extinction, physically moving them might be our only option," says Loarie, "but setting aside connected, heterogeneous landscapes that allow natural movement will almost certainly be an better use of conservation dollars."

    He and the other co-authors, including scientists at Climate Central in Palo Alto and the California Academy of Sciences in San Francisco, emphasize that their velocity maps are oversimplifications - at least so far. For one thing, they do not account for the unique characteristics of various species within a given ecosystem. Some species may have more tolerance for climate changes than others, and may not need to move as quickly; some species may be intolerant of change but unable to move. Other species may be sensitive to changes in rainfall, while still others responsive only to temperature - and changes in these weather patterns may not happen at the same rate. "The complexity is daunting," says Ackerly.

    Nevertheless, while the climate-velocity concept is still crude, it's promising enough that Ackerly is collaborating with an organization called the Bay Area Open Space Council on habitat conservation strategies in central California. The new research informs one of the key challenges conservationists face: having only limited funds to buy up land, and, thus, having to spend wisely. "What we bring," says Ackerly, "is the ability to think about how topography might affect those decisions."

    用以衡量氣候變化影響的單位有很多：qiwenshangshengdedushu，haipingmianshangshengdechishu，weishiyingzhegezaibiannuandeshijiesuoxuzhifudejinqianshu。ranerzaimeiguojiazhou，yixiekexuejiamenxinfaxianleyigeyouqudehengliangdanwei：千米數每年。

    在周三版《自然》雜(za)誌(zhi)上(shang)的(de)一(yi)篇(pian)文(wen)章(zhang)中(zhong)

，科(ke)學(xue)家(jia)描(miao)述(shu)了(le)他(ta)們(men)所(suo)謂(wei)的(de)氣(qi)候(hou)變(bian)化(hua)速(su)率(lv)，更(geng)確(que)切(qie)地(di)說(shuo)，是(shi)地(di)球(qiu)變(bian)更(geng)其(qi)氣(qi)候(hou)帶(dai)的(de)速(su)度(du)。科(ke)學(xue)家(jia)表(biao)示(shi)
，在(zai)下(xia)一(yi)世(shi)紀(ji)中(zhong)，隨(sui)著(zhe)全(quan)球(qiu)氣(qi)溫(wen)不(bu)斷(duan)上(shang)升(sheng)，地(di)球(qiu)上(shang)適(shi)宜(yi)居(ju)住(zhu)的(de)氣(qi)候(hou)帶(dai)也(ye)會(hui)有(you)所(suo)變(bian)動(dong)
，逐(zhu)漸(jian)遠(yuan)離(li)赤(chi)道(dao)向(xiang)兩(liang)極(ji)發(fa)展(zhan)。這(zhe)就(jiu)意(yi)味(wei)著(zhe)許(xu)多(duo)動(dong)植(zhi)物(wu)物(wu)種(zhong)若(ruo)要(yao)繼(ji)續(xu)存(cun)活(huo)就(jiu)必(bi)須(xu)遷(qian)移(yi)。它(ta)們(men)是(shi)否(fou)能(neng)夠(gou)存(cun)活(huo)與(yu)諸(zhu)多(duo)因(yin)素(su)密(mi)切(qie)相(xiang)關(guan)，其(qi)中(zhong)最(zui)重(zhong)要(yao)的(de)兩(liang)點(dian)是(shi)：該物種調整其棲息地範圍的速度，以及該範圍自身變化的速度。

    在zai這zhe以yi前qian

，生sheng態tai學xue家jia大da多duo關guan注zhu氣qi候hou變bian化hua的de各ge種zhong因yin素su對dui個ge體ti物wu種zhong的de影ying響xiang

，但dan是shi這zhe篇pian文wen章zhang更geng加jia綜zong合he地di從cong整zheng體ti的de視shi角jiao看kan問wen題ti。通tong過guo將jiang氣qi溫wen變bian化hua預yu測ce很hen好hao地di和he全quan球qiu地di形xing圖tu相xiang結jie合he，研yan究jiu人ren員yuan預yu言yan變bian化hua不bu會hui是shi個ge別bie物wu種zhong的de，氣qi候hou帶dai也ye將jiang產chan生sheng變bian化hua，這zhe也ye是shi他ta們men需xu要yao跟gen進jin的de。

    事實上，由於全球氣溫正在不斷上升，生態係統早已經開始變化了。"一旦你向人們解釋這個現象，它就有了直觀的意義。"合著者戴維·阿克利，來自加州柏克萊大學的一位生物學家說道，"我們知道向北發展以躲避氣溫的上升是怎麼一回事。它是具體的，而非抽象的平均氣溫上升。"

    除(chu)了(le)直(zhi)觀(guan)以(yi)外(wai)
，這(zhe)項(xiang)新(xin)的(de)指(zhi)數(shu)也(ye)被(bei)證(zheng)實(shi)是(shi)非(fei)常(chang)有(you)用(yong)的(de)，尤(you)其(qi)是(shi)對(dui)那(na)些(xie)致(zhi)力(li)於(yu)保(bao)護(hu)物(wu)種(zhong)免(mian)於(yu)滅(mie)絕(jue)的(de)環(huan)保(bao)主(zhu)義(yi)者(zhe)們(men)來(lai)說(shuo)。世(shi)界(jie)範(fan)圍(wei)內(nei)氣(qi)候(hou)變(bian)化(hua)所(suo)引(yin)起(qi)的(de)氣(qi)候(hou)帶(dai)平(ping)均(jun)變(bian)化(hua)速(su)率(lv)是(shi)略(lve)小(xiao)於(yu)0.5千(qian)米(mi)每(mei)年(nian)，然(ran)而(er)文(wen)章(zhang)還(hai)指(zhi)出(chu)，由(you)於(yu)各(ge)地(di)地(di)形(xing)不(bu)同(tong)，該(gai)數(shu)字(zi)很(hen)可(ke)能(neng)會(hui)有(you)較(jiao)大(da)幅(fu)度(du)的(de)浮(fu)動(dong)。在(zai)沙(sha)漠(mo)地(di)區(qu)以(yi)及(ji)其(qi)他(ta)平(ping)原(yuan)地(di)區(qu)
，如(ru)亞(ya)馬(ma)遜(xun)盆(pen)地(di)
，氣(qi)候(hou)帶(dai)的(de)變(bian)化(hua)會(hui)更(geng)快(kuai)，相(xiang)對(dui)而(er)言(yan)
，山(shan)區(qu)、丘陵地區比較緩慢。"比方說，在北半球，"主筆斯科特·勞瑞解釋到，"朝北的山坡往往比朝南的陰涼潮濕。"

    簡(jian)言(yan)之(zhi)，即(ji)便(bian)彼(bi)此(ci)靠(kao)得(de)很(hen)近(jin)，一(yi)座(zuo)山(shan)峰(feng)的(de)兩(liang)側(ce)也(ye)可(ke)能(neng)會(hui)有(you)不(bu)同(tong)的(de)氣(qi)候(hou)。因(yin)此(ci)，地(di)形(xing)多(duo)變(bian)的(de)地(di)區(qu)，包(bao)括(kuo)丘(qiu)陵(ling)地(di)帶(dai)，在(zai)相(xiang)對(dui)其(qi)比(bi)較(jiao)近(jin)的(de)地(di)方(fang)仍(reng)然(ran)可(ke)能(neng)找(zhao)到(dao)宜(yi)人(ren)的(de)環(huan)境(jing)。斯(si)坦(tan)福(fu)大(da)學(xue)卡(ka)耐(nai)基(ji)科(ke)學(xue)院(yuan)的(de)生(sheng)態(tai)學(xue)家(jia)勞(lao)瑞(rui)說(shuo)："我們沒有預料到是。在這多樣化的環境中其實還有很多的緩衝能力存在。"

    勞瑞和他的同事們繪製的變化速率地圖顯示，世界上僅有8%的de國guo家jia公gong園yuan以yi及ji其qi他ta自zi然ran保bao護hu區qu能neng在zai下xia個ge世shi紀ji保bao持chi其qi現xian有you的de氣qi候hou，這zhe也ye加jia劇ju了le如ru何he防fang止zhi物wu種zhong滅mie絕jue這zhe一yi問wen題ti的de嚴yan重zhong性xing。解jie決jue方fang案an之zhi一yi就jiu是shi遷qian移yi那na些xie麵mian臨lin瀕bin危wei的de物wu種zhong。然ran而er那na樣yang做zuo不bu僅jin異yi乎hu尋xun常chang地di困kun難nan，而er且qie可ke能neng產chan生sheng事shi與yu願yuan違wei的de結jie果guo--比如美國東南部人盡皆知的葛藤，該植物在被引進後攻擊性地大肆蔓延。"對一些瀕臨滅絕邊緣的物種進行物理遷移可能是我們唯一的選擇
，"勞瑞說
，"但是那些允許自然遷移的環境多樣性環境相互連接，如果撇開這些，那幾乎肯定是節省資金的更好的方法。"

    他(ta)以(yi)及(ji)其(qi)他(ta)的(de)合(he)著(zhe)者(zhe)們(men)，包(bao)括(kuo)帕(pa)洛(luo)阿(e)爾(er)托(tuo)氣(qi)候(hou)研(yan)究(jiu)中(zhong)心(xin)和(he)舊(jiu)金(jin)山(shan)加(jia)利(li)福(fu)尼(ni)亞(ya)科(ke)學(xue)院(yuan)的(de)科(ke)學(xue)家(jia)們(men)，他(ta)們(men)強(qiang)調(tiao)指(zhi)出(chu)，該(gai)變(bian)化(hua)速(su)率(lv)圖(tu)尚(shang)有(you)些(xie)過(guo)度(du)單(dan)純(chun)化(hua)，至(zhi)少(shao)目(mu)前(qian)是(shi)這(zhe)樣(yang)的(de)。首(shou)先(xian)，他(ta)們(men)沒(mei)有(you)對(dui)給(gei)定(ding)生(sheng)態(tai)係(xi)統(tong)中(zhong)各(ge)物(wu)種(zhong)的(de)自(zi)身(shen)特(te)征(zheng)做(zuo)出(chu)說(shuo)明(ming)。有(you)一(yi)些(xie)物(wu)種(zhong)可(ke)能(neng)比(bi)其(qi)他(ta)的(de)物(wu)種(zhong)對(dui)氣(qi)候(hou)變(bian)化(hua)具(ju)有(you)更(geng)強(qiang)的(de)適(shi)應(ying)性(xing)
，就(jiu)不(bu)需(xu)要(yao)迅(xun)速(su)轉(zhuan)移(yi)；還有一些物種雖然適應性也強
，但可能沒法遷移。一些物種可能在雨季會對變化非常敏感，而另一些隻會對溫度敏感--並且氣候的變化形式很可能不會總是以相同的比率發生。阿克利說："其複雜性令人望而生畏。"

    jinguanqihoubianhuasulvdegainianshangweichengshu
，danshimuqianekelizhengyuyigejiaozuohaiwandiqulvdiweiyuanhuidehezuo，tamenzhiliyuyanjiujialifuniyazhongbudiqujuzhudidehuanjingbaohuzhanlve，zheshifeichangzhenfenrenxinde。xindeyanjiuzhichuhuanbaozhuyizhemianlindezhuyaotiaozhanzaiyu：能用來盡量收購土地的資金非常有限，因此必須理智地花錢。阿克利說："我們能夠提供的是有能力去思考地形會如何影響到這些決策。"