如果可以在未來的幾十年內逐漸終止燒煤所排出的溫室氣體，燃燒其他化石燃料所排放的二氧化碳量，或許可以維持在不構成傷害的程度。 美國太空總署哥達德太空研究院（NASA Goddard Institute for Space Studies, GISS）院長，同時也是哥倫比亞大學地球學會成員的韓森博士（Dr. James Hansen）最近發表上述看法。
目前大氣中的二氧化碳濃度約是385ppm。而從前工業化時代以來大氣層中二氧化碳的增加量，大約有80%是由燃燒化石燃料而來。
韓森指出，當這個世界上還存有大量的煤炭，石油和天然氣的產出會在何時或是如何耗盡的預言，將引起很大的爭議，如此一來也讓我們更難去預測未來的溫室氣體排放量。
同時，對於少量的石油和天然氣，我們更應節約使用，根據韓森以及他的團隊最新出版的研究論文顯示，大量的煤炭供應意謂著：「煤碳」將是我們減少溫室氣體排放量的最主要目標。
為了了解未來溫室氣體排放量會如何變化，韓森和氣候學家卡連加（Pushker Kharecha），將1850年到2100年分成5個不同的情境。每一個情境都反映出全球化石燃料生產高峰的預測值，而時間點的畫分將依其存量多寡、可還原性以及開採技術而有所不同。
卡連加表示，「這是第一篇明確地指出二大關鍵議題的論文：全球石油生產高峰以及人類引起的氣候變遷。我們發現因為煤炭的蘊藏量比石油或天然氣還要豐富，因此降低燃煤排放量，絕對是避免氣候變遷危機的基本要件。」
第一個情境預測了二氧化碳的程度，如果化石燃料的排放量「一切如常」的每年成長2%，直到每一種現存煤炭的半數開始還原(recovered)，在這之後，溫室氣體排放量將開始每年減少2%。
第二種情境是，首先是由已開發國家在2013年開始減少燃煤排放量；再來是開發中國家，在10年之後也開始減少燃煤排放量；最後在2050年全球將可淘汰燃煤產生的溫室氣體排放量。這種情形可能由於減少煤炭消耗，或是在二氧化碳進入空氣之前，就捕捉或吸收這些二氧化碳。
剩下的三種情境包括，不再使用煤炭，但這必須考量石油在使用與供應的不同情境。另外一種可能是石油高峰延遲出現約21年，也就是到2037年才出現。
An ongoing rise in atmospheric levels of the greenhouse gas carbon dioxide emitted by burning fossil fuels might be kept below harmful levels if emissions from coal are phased out within the next few decades, says Dr. James Hansen, director of the NASA Goddard Institute for Space Studies, a member of Columbia University's Earth Institute.
Fossil fuel combustion accounts for about 80 percent of the rise of atmospheric CO2 since the pre-industrial era, to its current level of 385 parts per million.
While there are huge amounts of coal left, predictions about when and how oil and gas production might start running out have proved controversial, and this has made it difficult to anticipate future emissions, says Hansen.
Less plentiful oil and gas should be used sparingly as well, but based on their newly published research paper, Hansen and his team say that far greater supplies of coal mean that it must be the main target of emissions reductions.
To better understand how the emissions might change in the future, Hansen and climatologist Pushker Kharecha devised five emissions scenarios spanning the years 1850 to 2100.
Each reflects a different estimate for the global production peak of fossil fuels, the timing of which depends on reserve size, recoverability and available technology.
"This is the first paper that explicitly melds the two vital issues of global peak oil production and human-induced climate change," Kharecha said. "We found that because coal is much more plentiful than oil or gas, reducing coal emissions is absolutely essential to avoid dangerous climate change."
The first scenario estimates CO2 levels if emissions from fossil fuels follow "business as usual," growing two percent annually until half the existing reserve of each fuel has been recovered. After this, emissions begin to decline by two percent annually.
In the second scenario, emissions from coal are reduced, first by developed countries starting in 2013, and then by developing countries a decade later, leading to a global phaseout of emissions by 2050. The phaseout could come either from reducing coal consumption or by capturing and trapping CO2 from coal burning before it reaches the air.
The remaining three scenarios include the phaseout of coal, but consider different scenarios for oil use and supply. One case considers a delay in the oil peak by about 21 years to 2037.
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