Global warming 2007 - An update to global warming: The balance of evidence and its policy implications
Global warming 2007 - An update to global warming: The balance of evidence and its policy implications
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DOI：
10.1100/tsw.2007.91
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发表时间：
2007-01-01
影响因子：
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通讯作者：
Keller, Charles F.
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文献类型：
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作者：
Keller, Charles F.
在我最初的评论（Keller[25];以下简称CFK 03）之后的四年里，研究澄清并加强了我们对人类如何使地球变暖的理解。IPCC第三次评估报告[21]和CFK 03中强调的许多细节已经解决，我希望许多人都有点不知所措，我希望，通过处理研究中最重要的方面，这次更新可以提供一个路线图，通过预期的新信息迷宫。特别是，虽然CFK 03的大部分内容仍然是最新的，但有一些重要的内容已经发生了变化：最值得注意的是解决了对流层中部变暖似乎与地表变暖不匹配的难题。卫星和无线电探空仪（气球传感器）数据的减少表明，对流层中部（4-8公里高度）几乎没有变暖。在CFK 03中，我讨论了这个问题的潜在解决方案，但当时没有明确的解决方案。这个问题现在已经解决了，对流层中层与地表的变暖速度一样快。在过去1,000年里，对温度的测定也取得了进展，表明小冰期（LIA）的温度较低，但中世纪的变暖程度基本相同（没有最近的变暖那么大）。最近关于所谓的“曲棍球棒”温度测定的骚动被夸大了，因为至少有七个其他小组在同一时期对北方温度进行了相对独立的测定，并得出了基本相同的结果。他们对LIA有多冷有不同的看法，但基本上同意曼恩的曲棍球棒结果，即中世纪温暖期没有过去25年那么温暖。太阳对气候的影响问题继续产生争议。似乎越来越多的人一致认为，虽然太阳是早期温度变化的主要因素，但在过去的四分之一世纪左右，它无法引起观测到的变暖。然而，这一结论受到了对太阳总日照（TSI）卫星观测的不同解释的挑战。不同的卫星对1996- 1997年太阳活动极小期的TSI给出了不同的估计。最近的一项研究使用更大的TSI卫星解释表明，太阳的作用更大，在太阳极小期的TSI达成一致之前，我们警告完全忽视太阳作为近期变暖的重要因素。计算机模型继续改进，虽然它们仍然不能令人满意地预测区域变化，他们对全球气候变化和单个强迫的模拟越来越可靠。除了这四个领域，在过去的五年里，我们对气候变化的许多其他方面的理解都有了进步，从土地使用引起的气候变化到冰川运动的动力学。然而，这些更多的是次要的，只会非常简短地处理。自CFK 03以来的大新闻是其中的第一个，气候批评家最后一个真实的堡垒的崩溃，即卫星和无线电探空仪显示在过去的四分之一世纪没有明显的变暖。形象地说，这是支撑批评家整个“帐篷”的中心柱。“他们的论点是，如果在过去25年左右的时间里几乎没有变暖，那么观察到的变暖将在自然变化的范围内，太阳强迫是主要因素。此外，这些模型将被证明是不可靠的，因为它们预测的变暖并没有发生。但是现在卫星和现场无线电探空仪观测都证实了地面观测和模式预测的变暖。因此，尽管不确定性仍然存在，我们现在看到了一个连贯的画面，其中过去的气候变化，太阳和其他强迫，模型预测和其他指标，如冰川衰退都指向人类-最后一个简短的话题是对所谓“全球变暗”现象的新认识。“几组对太阳表面总辐射的观测表明，到达太阳表面的阳光已经减少。这与气溶胶对阳光的散射有关，并导致更好地量化清理我们的大气污染将导致更大的全球变暖的可能性。把所有这些进展加在一起，越来越多的人一致认为，21世纪确实会出现2摄氏度（3.5华氏度）或更多的额外变暖。这一点在新的IPCC评估中得到了证实，该评估的早期版本在这里非常简短地提到。
In the four years since my original review (Keller[25]; hereafter referred to as CFK03), research has clarified and strengthened our understanding of how humans are warming the planet. So many of the details highlighted in the IPCC's Third Assessment Report[21] and in CFK03 have been resolved that I expect many to be a bit overwhelmed, and I hope that, by treating just the most significant aspects of the research, this update may provide a road map through the expected maze of new information. In particular, while most of CFK03 remains current, there are important items that have changed:Most notable is the resolution of the conundrum that mid-tropospheric warming did not seem to match surface warming. Both satellite and radiosonde (balloon-borne sensors) data reduction showed little warming in the middle troposphere (4-8 km altitude). In the CFK03 I discussed potential solutions to this problem, but at that time there was no clear resolution. This problem has now been solved, and the middle troposphere is seen to be warming apace with the surface.There have also been advances in determinations of temperatures over the past 1,000 years showing a cooler Little Ice Age (LIA) but essentially the same warming during medieval times (not as large as recent warming). The recent uproar over the so-called "hockey stick" temperature determination is much overblown since at least seven other groups have made relatively independent determinations of northern hemisphere temperatures over the same time period and derived essentially the same results. They differ on how cold the LIA was but essentially agree with the Mann's hockey stick result that the Medieval Warm Period was not as warm as the last 25 years.The question of the sun's influence on climate continues to generate controversy. It appears there is a growing consensus that, while the sun was a major factor in earlier temperature variations, it is incapable of having caused observed warming in the past quarter century or so. However, this conclusion is being challenged by differing interpretations of satellite observations of Total Solar Insolation (TSI). Different satellites give different estimates of TSI during the 1996-7 solar activity minimum. A recent study using the larger TSI satellite interpretation indicates a stronger role for the sun, and until there is agreement on TSI at solar minimum, we caution completely disregarding the sun as a significant factor in recent warming.Computer models continue to improve and, while they still do not do a satisfactory job of predicting regional changes, their simulations of global aspects of climate change and of individual forcings are increasingly reliable.In addition to these four areas, the past five years have seen advances in our understanding of many other aspects of climate change-from albedo changes due to land use to the dynamics of glacier movement. However, these more are of second order importance and will only be treated very briefly.The big news since CFK03 is the first of these, the collapse of the climate critics' last real bastion, namely that satellites and radiosondes show no significant warming in the past quarter century. Figuratively speaking, this was the center pole that held up the critics' entire "tent." Their argument was that, if there had been little warming in the past 25 years or so, then what warming was observed would have been within the range of natural variations with solar forcing as the major player. Further, the models would have been shown to be unreliable since they were predicting warming that was not happening. But now both satellite and in-situ radiosonde observations have been shown to corroborate both the surface observations of warming and the model predictions.Thus, while uncertainties still remain, we are now seeing a coherent picture in which past climate variations, solar and other forcings, model predictions and other indicators such as glacier recession all point to a human-induced warming that needs to be considered carefully.A final topic touched on briefly here is the new understanding of the phenomenon called "global dimming." Several sets of observations of the sun's total radiation at the surface have shown that there has been a reduction in sunlight reaching it. This has been related to the scattering of sunlight by aerosols and has led to a better quantification of the possibility that cleaning up our atmospheric pollution will lead to greater global warming.Adding all these advances together, there is a growing consensus that the 21st century will indeed see some 2 degrees C (3.5 degrees F) or more in additional warming. This is corroborated in the new IPCC Assessment, an early release of which is touched on very briefly here.