Global warming could be reversed used a combination of burning trees and crops for energy, and capturing and storing carbon dioxide underground (CCS), according to an analysis by scientists. But experts cautioned that trying such an approach after temperatures had passed dangerous levels could be problematic, as climate change reduced the number of trees available for "bioenergy".
The bioenergy and CCS method was the most cost-effective way of tackling carbon emissions, said the team Chalmers University of Technology in Sweden, publishing their research in the journal Environmental Research Letters on Thursday. Such an approach could offset and even reverse other emissions from fossil fuels, they claimed.
The lead author of the study, Prof Christian Azar, said it could help bring temperatures down even if they rose above the 2C level that world leaders have agreed to avoid: "Even if current political gridlock causes global warming in excess of 2C, we can reverse the temperature trend and reach targets later. This means that 2C targets, or even more ambitious targets, can remain on the table in international climate negotiations."
He said that to achieve a reversal of temperatures, the combination of bioenergy and CCS would need to be combined with a huge expansion in renewable energy or nuclear power, in order to reduce emissions almost to zero. He also admitted that there was a political risk that the proposal's ability to reverse rises at a late stage could be used as an excuse for short-term inaction on emissions.
CCS technology has been tested successfully on small-scale trials, but is still unproven at commercial scale anywhere in the world. Environmentalists have also questioned the carbon benefits of burning trees for power, saying that in some cases the "lifecycle" emissions are worse than coal.
Dr Vivian Scott of Scottish Carbon Capture Storage at the University of Edinburgh, who was not involved with the research, said that the basis for the research's conclusion was sound, but he warned it should not be interpreted "as a 'get out of jail free' card in 50 years' time" and the idea could be hamstrung by climate change itself.
"As shown in this work, Beccs [Bioenergy with Carbon Capture and Storage] could offer a way back from exceeding climate targets. However, there are potentially huge consequences to allowing an overshoot [of those targets]. A warmer climate for even a limited period could profoundly alter meteorological and ecological systems – changes which could perhaps even restrict the ability to produce the biomass on which we might be reliant to reduce the atmospheric carbon dioxide content," he said.
He also said that reducing carbon emissions to zero could be a major challenge, given the track record of previous efforts to cut carbon: "Progress in addressing emissions has been woefully slow - the International Energy Agency recently announced that the average amount of carbon dioxide produced for each unit of energy generated has barely changed in the period 1990 - 2010 … in essence all the emissions mitigation efforts to date have achieved almost nothing".
据《卫报》7月11日报道，根据科学家的一份分析报告，通过混合燃烧树木和农作物获得 的能量和利用碳捕捉与封存技术（CCS）也许可以倒转全球变暖。但是，科学家警告，温度已经超过警戒线，现在尝试这个方法可能会有问题，因为气候变化减少 了释放“生物能”（Bioenergy）的树木数量。
瑞典查尔姆斯理工大学研究团队表示，生物能与碳捕捉与封存技术是解决碳排放问题成本效 益最好的方法。他们7月11日在《环境研究快报》（Environmental Research Letters）期刊上发表了相关研究论文。他们宣称这个方法能抵消甚至倒转矿物燃料的其他排放量。
该项研究的第一作者克里斯蒂安·阿扎教授（Prof Christian Azar）表示，全球领袖一致同意温度应该控制在2C水平以内，即使温度超过2C水平，这个方法也可以使温度降低。他说：“即使最近的政治僵局导致全球变 暖，温度超过2C水平，我们仍可以倒转这一温度上升趋势，使其不久后下降到2C水平。这意味着温度保持在2C水平这一目标，或者更远大的目标可以继续成为 国际气候谈判的话题。”
他表示，为了达到温度的倒转，除了使用生物能和二氧化碳捕捉与封存技术，我们还需要大量膨胀可再生能源或核能，这样可以把二氧化碳排放量几乎减少为零。他也承认，这个计划存在一定的政治风险，在后期阶段，该计划倒转全球变暖的能力可能会被用作排放问题短期互动的借口。
碳捕捉与封存技术已在小型试验中测试成功，但是，该技术目前尚未在世界各地商业领域使用。环境学家也质疑燃烧树木获取能量的碳效益，表示在一些例子中，“生命周期”排放比煤排放效果更差。
该研究项目参与者爱丁堡大学研究苏格兰碳捕捉与封存的维维安·斯科特博士表示这项研究结论的基础相当扎实，但是，他警告，这并不一定是最佳解决方案，这个主意也有可能被气候变化本身所毁掉。
他说：“正如这项研究所示，Beccs（生物能结合碳捕捉与封存技术）可以提供技术支 持，以保证温度在气候目标范围内。但是，过分强调（那些目标）有可能造成严重的后果。短时间内气候变暖可能深深地改变气象和生态系统——这种改变甚至可能 限制生物量的产生。我们也许要依赖于生物量从而减少大气中二氧化碳的含量。”
他还提到，根据过去努力减少碳排放的记录，零碳排放是很大的挑战：“不幸的是，处理碳 排放问题一直以来进度缓慢——国际能源署（International Energy Agency）最近公布，1990年至2010年，每单元能量产出的二氧化物的汽化器平均数量几乎没有改变……大体上，至今所有的减排努力几乎没有成 果。”