A recent article in the Guardian reported that 2012 saw the second highest annual rise in CO2. This was 2.67 parts per million (ppm) measured at the Mauna Loa Observatory on Hawaii. The article also included a link to a paper published in Science that presented reconstructions of regional and global temperature for the past 11,300 Years (Marcott et al., 2013, Science, 339, 1198-1201).
It seems as though many who are skeptical (deny) man-made climate change often say things like “where is the paper that says ….”, so I thought I would highlight some of the results presented in this paper. Below I reproduce the abstract. Quite a balanced abstract containing a summary of the results and a conclusion, at the end, that suggests that by 2100 the global surface temperatures will be higher than at any time in the past 11,300 years.
Surface temperature reconstructions of the past 1500 years suggest that recent warming is unprecedented in that time. Here we provide a broader perspective by reconstructing regional and global temperature anomalies for the past 11,300 years from 73 globally distributed records. Early Holocene (10,000 to 5000 years ago) warmth is followed by ~0.7°C cooling through the middle to late Holocene (<5000 years ago), culminating in the coolest temperatures of the Holocene during the Little Ice Age, about 200 years ago. This cooling is largely associated with ~2°C change in the North Atlantic. Current global temperatures of the past decade have not yet exceeded peak interglacial values but are warmer than during ~75% of the Holocene temperature history. Intergovernmental Panel on Climate Change model projections for 2100 exceed the full distribution of Holocene temperature under all plausible greenhouse gas emission scenarios.
Below is one of the main figures from the paper. It shows the temperature anomaly and compares various different methods. The left-hand panel goes back 2000 years, while the right-hand panel goes back 11,300 years. There is good agreement between the different methods and it seems clear that the temperature anomaly today is higher than it has been for the past 2000 years.
It, however, appears (from the righ-hand panel in the above figure) that there may have been periods during the Holocene when the temperature may have been higher than it is today. However, I include – below – some of the concluding text from the paper.
Our results indicate that global mean temperature for the decade 2000–2009 (34) has not yet exceeded the warmest temperatures of the early Holocene (5000 to 10,000 yr B.P.). These temperatures are, however, warmer than 82% of the Holocene distribution as represented by the Standard5×5 stack, or 72% after making plausible corrections for inherent smoothing of the high frequencies in the stack (6) (Fig. 3). In contrast, the decadal mean global temperature of the early 20th century (1900–1909) was cooler than >95% of the Holocene distribution under both the Standard5×5 and high-frequency corrected scenarios. Global temperature, therefore, has risen from near the coldest to the warmest levels of the Holocene within the past century, reversing the long-term cooling trend that began ~5000 yr B.P. Climate models project that temperatures are likely to exceed the full distribution of Holocene warmth by 2100 for all versions of the temperature stack (35) (Fig. 3), regardless of the greenhouse gas emission scenario considered (excluding the year 2000 constant composition scenario, which has already been exceeded). By 2100, global average temperatures will probably be 5 to 12 standard deviations above the Holocene temperature mean for the A1B scenario (35) based on our Standard5×5 plus high-frequency addition stack (Fig. 3).
Probably the strongest statement is that within the past century global average temperatures have gone from some of the coolest of the last 11,300 years to some of the warmest. If this continues, as is expected, by 2100 global average temperatures will be significantly higher than the mean of the Holocene. Here we have a very recent peer-reviewed paper in a major scientific journal saying that within the next 100 years, average global temperatures will be higher than they’ve been for the last 11,300 years. The paper doesn’t actually say that such high temperatures could have a catastrophic effect on man, but I think we can probably conclude that it won’t be ideal.