Second fastest annual rise in carbon dioxide

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.

Comparison of various methods for determining the temperature anomaly for the past 2000 years (left-hand panel) and for the last 11,300 years (right-hand panel).  Figure from Marcott et al. (2013).

Comparison of various methods for determining the temperature anomaly for the past 2000 years (left-hand panel) and for the last 11,300 years (right-hand panel). Figure from Marcott et al. (2013).

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.


10 thoughts on “Second fastest annual rise in carbon dioxide

  1. You may wish to revisit your claims in defense of the Marcott et al. paper. The data in Marcott’s Ph.D. thesis do not show the hockey stick uptick found in the Science article despite being the same data. Marcott has recently emailed Steve McIntyre that the uptick may not be “robust”. Furthermore, McIntyre has detailed at the questionable statistical techniques employed by Marcott et al. The article is poor science with flawed statistical methodologies. It should be retracted.

    • I guess we’ll have to wait and see. You could try reading this post that rebuts much of the criticism of Marcott et al. I haven’t looked through the data or analysis in great detail myself, so can’t claim that I completely understand the criticism or the rebuttal. I was, however, rather confused by the criticism focusing mainly on the last 100 years. We have extensive measurements that show the temperature anomaly increasing by about 1oC since 1880, so the uptick in the Marcott et al. paper seems entirely consistent with this.

  2. Read the post you suggested, thank you. Unfortunately, it is argumentum ad hominem and does not address the science at issue; however, the authors of the paper in question (i.e., Marcott et al.) have recently posted an online FAQ regarding their contentious work: In their own words the authors repeat what I stated on March 18: “Thus, the 20th century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes….” The selective statistical methodologies used in the article are dubious and do not support the conclusion that temperatures are warmest today during the entire Holocene. Furthermore, Marcott’s own Ph.D. Dissertation data does not support the article because different statistical techniques were employed.

    • I’ve read most of what I’ve found about this paper, so I have a few comments. The main aim of the work (as far as I’m aware) was to produce temperature anomalies from the Holocene until know. This is new as noone has done something like this before. The resolution isn’t particularly good and so their 20th century portion is not robust. However, we know from instrumental data that there has been a rise of about 1o C since about 1900. The total variation over the last 110000 is only about 0.8 degrees C and so a rise of 1 degree C in the last century is quite significant. Having said that, their resolution does mean that they can’t rule out short term spikes in the temperature anomaly in earlier periods. However, if the temperature anomaly continues to increase, their work suggest that it will soon be hotter today than it has been for the last 110000 years. Essentially what I’m suggesting is that the significance of their work is not the 20th century portion, but is the data going back to the Holocene. I accept that there will always be issues with this type of analysis. The resolution we have today is very different to what one can achieve using proxies. The authors, however, make this quite clear and I find it frustrating that when climate scientists acknowledge these kind of issues these then get used to claim that there are major problems with their work.

      I must admit that I find comparing the thesis and the paper is an odd thing to do. I work in academia and it’s not unusual to submit work at the same time (or after) completing a thesis and to end up publishing something that differs from what the thesis says. The referee of the paper may not know of the thesis. The thesis examiner may notice an issue but not make a big deal of it if they think that it’s unreasonable to expect someone to repeat a lot of work. The thesis and the paper are two different things and one can’t argue that the paper is wrong simply because it differs from the thesis.

    • Thanks, TTLC for the h/t.

      To Francesco Liposo: I find it strange that you consider criticism, such as of tacking the Marcott et al reconstruction onto minus 30 degree temperatures of the ice sheet in Central Greenland, to be “argumentum ad hominem“.

      I’d say either you didn’t “Read the post” or you do not know the meaning of “argumentum ad hominem“.

      • Thanks for the comment. I’ve been reading some of your other posts. Quite interesting.

        I was also slightly surprised by Francesco’s comment that your post was argumentum ad hominem. It was certainly a lot less ad hominem than a typical Watts up With That post. It’s also hard not to be a little personal when rebutting criticism of a piece of work and I thought you addressed the science well.

      • Thanks to a comment you made on another blog (or article) I’ve found this post on Real Climate. For those who don’t know, it’s a commentary and FAQ prepared by the authors of Marcott et al. I think it’s quite clear and informative and well worth a read. Maybe Francesco would like to read it and give his thoughts.

  3. Thanks, yes HotWhopper is my snark blog not my science blog. It’s a mix of poking fun at the silliest points made by science deniers and looking at some of the psychology of denial. And because it’s snark and not seriously academic (though a bit of sciency stuff creeps in sometimes), I say what I think of the people who spread disinformation. Confirmation bias by deniers could easily confuse that with ad hom – but the difference is my opinion is based on what they say and do, not things unassociated with the subject at hand.

    Sometimes, though ad hom is valid. For example, I just found out that Ross McKitrick’s religion doesn’t accept evolution or climate science, which would explain a lot why he denies climate science (and presumably biology, geology and various other related sciences). Roy Spencer is a member as well, which probably explains his odd stance even though in his day job he documents global warming. (Both are listed as being on the advisory board of a cult called the Cornwall Alliance which is based somewhere in North America).

    Still, in the end it doesn’t matter why they don’t accept the evidence unless they have very good scientific grounds to dispute it. When it’s for religious reasons then it helps clarify for non-scientists that the basis for their opposition is not scientific. (A bit like people being able to opt out of vaccinations on religious, not scientific grounds. And like Anthony Watts admitting on PBS that he decided to reject science when he realised it might have a policy implication he doesn’t agree with.)

    • Interesting. I was just in the process of writing a post about Ross McKitrick when you made your comment. It’s now finished. If you felt like adding a comment on that post, you would be most welcome.

  4. Pingback: The Economics of Climate Change | To the left of centre

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s