U.S. forests could worsen global warming instead of easing it because they are being destroyed by natural disasters and are losing their ability to?absorb?planet-warming gases as they get older, a new Agriculture Department report says.

美國農(nóng)業(yè)部的一份新報告稱，美國的森林正在遭受自然災害的破壞，隨著年齡的增長，它們正在失去吸收溫室氣體的能力，這可能會加劇全球變暖，而不是緩解全球變暖。

The report predicts that the ability of forests to absorb carbon will start?plummeting?after 2025 and that forests could?emit?up to 100 million metric tons of carbon a year as their emissions from?decaying?trees?exceed?their carbon absorption. Forests?could become a “substantial carbon source” by 2070, the USDA report says.

這份報告預測，森林吸收二氧化碳的能力將在2025年之后開始急劇下降，而且由于樹木腐爛排放的碳量超過了它們能吸收的量，森林每年將釋放1億噸的碳（二氧化碳）。美國農(nóng)業(yè)部的報告表示，到2070年，森林將成為一個“重大的碳源”。

U.S. forests currently absorb 11 percent of U.S carbon emissions, or 150 million metric tons of carbon a year,?equivalent?to the combined emissions from 40 coal power plants, the report says.The prediction suggests that the loss of forests as a natural carbon absorber will require the U.S. to cut emissions more rapidly to reach net zero, said Lynn Riley, a senior manager of climate science at the American Forest Foundation, a nonprofit conservation advocate not?involved in?the USDA report.

報告說，美國森林目前吸收了美國11%的碳排放量，即每年1.5億噸碳，相當于40座燃煤電廠的總排放量。美國森林基金會氣候科學高級經(jīng)理林恩·萊利說，這一預測表明，森林作為一種天然的碳吸收器，它的逐漸消失將要求美國更快地減少排放，才能達到凈零排放目標。美國森林基金會是一家非營利性的環(huán)保倡導機構，未參與到美國農(nóng)業(yè)部的此項報告中。

The USDA report published Monday assesses and predicts the extent of?renewable?resources provided by the nation’s forests and undeveloped landscapes, including farmlands, wetlands and grasslands. The?decennial?report is mandated by Congress, which in 1990 added a requirement to study climate impacts on forests and?rangelands.

美國農(nóng)業(yè)部周一發(fā)布的報告評估并預測了美國森林和未開發(fā)景觀(包括農(nóng)田、濕地和草原)能提供可再生資源的程度。這份十年一度的報告由國會授權，國會1990年增加了一項研究氣候對森林和牧場影響的要求。

The loss of carbon absorption is driven in part by natural disasters such as wildfires,?tornadoes?and?hurricanes, which are increasing in frequency and strength as global temperatures rise. The disasters destroy forestland, disrupting their ecosystem and decreasing their ability to absorb carbon, Riley said.?Development in forested areas, which the report projects will continue to increase, is having the same effect as people increasingly move to the so-called wildland urban?interface.

森林碳吸收能力的減少部分原因在于野火、龍卷風、颶風等自然災害，隨著全球溫度升高，這些災害的發(fā)生頻率和強度也在增加。萊利表示，這些災害摧毀了林地，破壞了它們的生態(tài)系統(tǒng)，降低了碳吸收能力。這份報告預測，隨著人們越來越多地選擇遷移到所謂的荒地和城市交接處，森林地區(qū)的開發(fā)將繼續(xù)增加，也會產(chǎn)生同樣的影響。