It’s back. The Pause has returned – at least it has in the satellite data over land. Sea surface temperatures are currently cooling quite rapidly and we can expect the global surface temperature Pause, or Hiatus, to re-establish itself some time in 2017. Which is not good news for climate change alarmists, especially coming on top of all the other bad news emanating from the political sphere. The latest talk is that arch climate denier Trump will starve NASA’s environmental science division of funding and plow the money into space exploration instead. Terrible. Gavin will not be happy.
What is interesting (to me at least, putting aside the politics for a change) is that decent science is now emerging to expand upon the current long list of excuses for the Pause, or Hiatus, or slowdown – which have mainly tended to focus on heat being swallowed up by the deep oceans or the influence of natural decadal climate variability. Of course, there have also been several ‘scientific’ attempts to erase the Pause completely using statistical arguments and/or ‘adjusted’ data. But it’s a stubborn bugger, this Pause, and its return is likely to cause considerable consternation in ze warmist bunker.
So, rather than ‘excuses’ which suggest a temporary slowdown in surface warming, we now have a scientific paper which actually posits a quite reasonable argument for believing that the Pause is a real, physical phenomenon, and not an insignificant one in terms of current and future climate change projections and hence climate change policy. A Hiatus of the Greenhouse Effect, Song, Wang, Tang, 2016:
The rate at which the global average surface temperature is increasing has slowed down since the end of the last century. . . . . .
The atmospheric and surface greenhouse effect over the tropical monsoon-prone regions is found to contribute substantially to the global total. Furthermore, the downward tendency of cloud activity leads to a greenhouse effect hiatus after the early 1990s, prior to the warming pause. Additionally, this pause in the greenhouse effect is mostly caused by the high number of La Niña events between 1991 and 2014. A strong La Niña indicates suppressed convection in the tropical central Pacific that reduces atmospheric water vapor content and cloud volume. This significantly weakened regional greenhouse effect offsets the enhanced warming influence in other places and decelerates the rising global greenhouse effect. This work suggests that the greenhouse effect hiatus can be served as an additional factor to cause the recent global warming slowdown. . . . . .
We represent an alternative pathway of internal variability driving the warming slowdown. A La Niña-like state suppresses convection in the tropical central Pacific and concomitantly reduces cloud coverage. Consequently, a zero-trend greenhouse effect is achieved under the balance of its primary contributors (e.g. water vapor, clouds, and GHGs). Finally, the hiatus of the greenhouse effect-driven warming leads to the recent global warming slowdown, in which the atmosphere traps (emits) near constant heat from (to) the surface.
Basically, what this paper is saying is that decreasing cloud cover in the central tropical Pacific region from 1992 to 2014 has reduced the (enhanced – i.e. water vapour included) atmospheric greenhouse effect in that region, which has offset increases elsewhere in the enhanced greenhouse effect. ‘Oh, that’s just natural internal variability’, hopeful warmists might say, ‘soon to be overridden by continuously increasing anthropogenic GHGs’. Alas, no, it is actually a negative feedback caused by warming in the first place, which suggests that warming will not occur at the rapid rates predicted by climate models, meaning that climate sensitivity is at the low end of current estimates. The text strongly suggests that this negative feedback mechanism is at play, even though it is careful not to say so explicitly:
The results above indicate that the notably downward Gaa tendency over the central tropical Pacific indeed plays an important role in inducing the greenhouse effect hiatus since the 1990s. What causes this decreasing Gaa? The variation of the greenhouse effect is substantially influenced by its contributors, including water vapor, clouds, and GHGs. GHG concentrations have risen steadily during recent decades . . . . .
The total column precipitable water (TCPW) anomaly significantly increases at a rate of 0.44 cm yr−1. However, the cloud area fraction (CAF) anomaly is reduced by − 0.60% yr−1, which is consistent with the decreasing cloud activity described in previous publications. Therefore, although the greenhouse effect can be enhanced by increasing GHGs and water vapor in the atmosphere, it can be weakened by decreasing clouds. If these two actions offset each other, a hiatus of the global greenhouse effect will result.
Another study published on November 8th must be even more worrying for climate alarmists – worrying in the more mundane sense that is, as they are, obviously, constantly consumed by a more esoteric and far-reaching concern for the future of the planet. This paper suggests that the earth system is actually responding to increasing anthropogenic CO2 by absorbing it at an enhanced rate. Carbon sinks – oceans/ biosphere – have supposedly doubled their uptake of CO2 in the last 50 years. The implications are far-reaching, to say the least. Rather than the linear increase in atmospheric carbon dioxide directly related to emissions which is currently assumed, CO2 might actually increase very much more slowly as the global carbon cycle adapts to the initial rapid increase by absorbing excess carbon into sinks at an enhanced rate. Let us also not forget that the fairly modest total increase in atmospheric CO2 post-industrial revolution is tiny in comparison to the available capacity of terrestrial sinks.
However, for the period 2002–2014 there has been no significant increase in the growth rate of CO2 (Fig. 1a and Supplementary Fig. 1). The decline in the airborne fraction since the start of the twenty-first century has therefore been sufficiently large as to result in a pause in the rate of increase of the atmospheric CO2 growth rate . . . . .
The slowing of the growth rate of atmospheric CO2 between 2002 and 2014 (Fig. 1a and Supplementary Fig. 1) coincides with a period during which global temperature increases over vegetated land also slowed markedly (Fig. 3 and Supplementary Fig. 3, note recent reports suggest continued warming over oceans). Since the start of the century, global temperatures over vegetated land increased at a rate of 0.1 _C per decade, compared with a rate of 0.32 _C per decade in the previous two decades (Fig. 3). Satellite-driven estimates of the carbon cycle suggest that the slowdown in global warming led to a slowdown in temperature-driven ecosystem respiration of roughly 60% (Fig. 3). . . . .
Although a lack of temperature increases likely contributed to the slowdown in the growth rate of atmospheric CO2 over the past decade (Fig. 3), results from the DGVM ensemble suggest that an increasing atmospheric CO2 concentration was the primary driver of the enhanced uptake over the past century (Fig. 4).
Thus we have another ‘Pause’ to accompany the Pause in global surface warming. Furthermore, this Pause in the rate of accumulation of CO2 in the atmosphere has been precipitated by 1) the Pause in global surface temperature, and 2) the observed increase in atmospheric CO2. You might expect that this would mean we now don’t have to worry so much about the effect of emissions on climate because global temperatures have slowed in addition to the more important fact that carbon is being sucked out of the atmosphere at a faster rate as plants adapt to increasing concentrations. But the authors don’t quite see it this way:
The slowdown in global warming is expected to be temporary however and may already have ended with the strong El Nino Southern Oscillation of 2015 and 2016, with subsequent consequences for the growth rate of atmospheric CO2 (ref. 36). The likely continuation of warming in the coming decades suggests further future increases in net carbon releases.
However, as we have seen, the Pause is back (as ENSO rapidly fades), negative cloud feedbacks may limit further global warming (as they have likely already done so far in the 21st century), climate sensitivity may thus be low, and if plant life and the oceans are also gobbling up anthropogenic CO2 at an increasing rate, the prospects for further ‘dangerous’ GHG warming are looking somewhat diminished. This is all very good news, but I suspect it will not be seen as such by advocates of runaway global warming, which is a little odd, given that the world is probably not as imperiled as they had hitherto ‘sincerely’ believed.