Sentences with phrase «very high climate sensitivity»

Yes, but we have no reliable methods for inferring very high climate sensitivity, other than climate models that are demonstrably running to hot and dubious analyses of the paleoclimate record.

However, from a purely policy standpoint, it is important to consider all possible scenarios, and a very high climate sensitivity can not yet be ruled out, as Chris Colose explains (via personal communication):

The orange line in Fig. 3 shows how strongly the IPCC's favoured use of a uniform prior in sensitivity dominates a not very informative likelihood function, giving the appearance of a high probability of a very high climate sensitivity that is very largely a reflection of the prior distribution used.

The calculated impact, based on IPCC assumptions, is likely to be on the high side, in view of the very high climate sensitivity assumed for the calculation (the actual temperature / CO2 record shows us it is high by a factor of 2 to 4).

I believe they will maintain the position that very high climate sensitivity is plausible, no matter what.

If aerosol forcing is high, then reconciling with recent warming demands very high climate sensitivity (which you see realized after the aerosols go away)-- and that would indeed mean we may have already passed the threshold for 2C warming.

The fact that even model versions with very high climate sensitivities pass their test does not show that the real world could have such high climate sensitivity; it merely shows that the test they use is not very selective.

«Our study shows that very high climate sensitivities are virtually impossible, suggesting that we still have enough time to deal with the problem and reduce carbon emissions, which could avoid the most severe impacts,» said Andreas Schmittner, a climate scientist at Oregon State University and the study's lead author.

«We can rule out very low climate sensitivities that might imply you don't need to do very much at all but also very high climate sensitivities that would be very difficult to adapt to.

The 95 percent confidence range in this study was between about 1 and 7 °C equilibrium sensitivity, so very low and very high climate sensitivities could not be ruled out, but are relatively unlikely, based on the historical record.

The main point of that paper was that very high climate sensitivities could be excluded by the LGM temperature reconstructions and I still think that this is a robust and important conclusion.

Not exact matches

Thus it is very important to know what the real impact of historical solar changes is, as 0.1 K in the past, results in climate sensitivity for anthropogenic at the high end, while 0.9 K results in a very low effect of anthropogenic, if the instrumental temperature trend of the last 1.5 century is used as reference.

For example, we know the past CO2 radiative forcing to very high accuracy, but there are more uncertainties in the aerosol forcing; applying a consistent climate sensitivity to both CO2 and aerosols, you can get a match to the observed record for a range of different supposed aerosol forcings, but you can't take it too far.

Then on page 9.5 we read «There is very high confidence that the primary factor contributing to the spread in equilibrium climate sensitivity continues to be the cloud feedback.

The fact that temperatures have been very high when CO2 was low and vice versa suggest a weak causal relationship, i.e. a low climate sensitivity.

But I understand sea level rise right now is actually towards the upper end of estimates so this suggests either climate sensitivity is towards the high end, or ice sheets are very sensitive to low or medium climate sensitivity.

First, how do you reconcile a high climate sensitivity (say 3 - 5 C / doubling) with the fact that there is very low correlation between CO2 and climate in the 500 million time scale?

Aslo, regarding climate sensitivity a very key thing to remember, especially if sensitivity turns out to be on the high side, is that the «final» equilibrium temperature (Alexi's concerns about there being such a thing aside) calculated from climate sensitivity does not take into account carbon cycle feedbacks OR ice sheet changes.

The physics tells us that it is much easier to get an Earthlike climate with a high sensitivity than it is with a very low sensitivity.

But Annan and Hargreaves have argued that this gives too much weight to very high values of climate sensitivity — after all, it makes no sense to assume as a prior that climate sensitivity of 3 deg.

The high end of current estimates for climate sensitivity are already in very negative and serious terratory.

The IPCC range, on the other hand, encompasses the overall uncertainty across a very large number of studies, using different methods all with their own potential biases and problems (e.g., resulting from biases in proxy data used as constraints on past temperature changes, etc.) There is a number of single studies on climate sensitivity that have statistical uncertainties as small as Cox et al., yet different best estimates — some higher than the classic 3 °C, some lower.

Although the sensitivity of climate does change itself as the boundary conditions change, the past (PETM, glacial - interglacial cycles, etc) does not support sensitivities as low as 1 degree per doubling of CO2, and it doesn't support very high ones (like 10 degrees per doubling) either.

That finding, supported by Forest 2006 Fig.S.7, means that the SFZ 2008 surface model data on their own provide very little discrimination against high climate sensitivity, unlike the CSF 2005 data.

In this light paleo research is very important too — as indeed when one looks at high - CO2 warm periods (for instance in the Tertiary) some data seems to suggest a climate sensitivity that would be somewhat higher than the IPCC range.

The magnitude of climate change beyond the next few decades will depend primarily on the amount of greenhouse (heat - trapping) gases emitted globally and on the remaining uncertainty in the sensitivity of Earth's climate to those emissions (very high confidence).

Finally, we have not yet taken note here of Shindell»14 «Inhomogeneous forcing and transient climate sensitivity» which makes a very strong case not only for the unexpected aerosol loading from China being the culprit for the divergence, but also, unfortunately, for the case that a rather high sensitivity is a logical consequence of that explanation.

Equilibrium climate sensitivity is likely in the range 1.5 °C to 4.5 °C (high confidence), extremely unlikely less than 1 °C (high confidence), and very unlikely greater than 6 °C (medium confidence)(Note 16).»

However, I am not a «warmista» by any means — we do not know how to properly quantify the albedo of aerosols, including clouds, with their consequent negative feedback effects in any of the climate sensitivity models as yet — and all models in the ensemble used by the «warmistas» are indicating the sensitivities (to atmospheric CO2 increase) are too high, by factors ranging from 2 to 4: which could indicate that climate sensitivity to a doubling of current CO2 concentrations will be of the order of 1 degree C or less outside the equatorial regions (none or very little in the equatorial regions)- i.e. an outcome which will likely be beneficial to all of us.

You are correct that climate sensitivity is probably more uncertain than to < 10 %, however there is a substantial literature on why it is very likely greater than 1.5 - 2 C per doubling of CO2, while ruling out higher end values of climate sensitivity is much more difficult.

FWIW it is my prejudice that the AR4 claim «very likely» «most of the warming» etc. is sufficiently weak to be safe against arguments that do not rely on very high sensitivities e.g. a random walk, with the possible exceptions of some unappreciated dominant forcing or that old standby that «the climate is chaotic to a degree that permits all possible outcomes».

I think James» point about the last decade is not that global warming has stopped (implying low or zero climate sensitivity) but that it has not accelerated to the extent that it would have if climate sensitivity were very high (above, say, 4).

Composer @ 1 - yes, it appears that contrarians interpreted Annan's comments as «climate sensitivity is not very high, therefore it's low».

I was under the impression that AR4 assigned a very high probability (> 90 %) to the climate sensitivity being in the range of 1.5 to 6 deg / doubling.

The very long tail of that distribution reflects partly poor data constraints and partly the use of a uniform prior for climate sensitivity, which biases upwards the reported probability of high climate sensitivities.

Gavin's refusal to admit the extreme LU efficacy comes down to accepting one very dubious run, a run which is a clear statistical outlier, goes to the heart of the problem with Marvel et al: the authors got results they «liked» (lower efficacy for many forcings implies higher climate sensitivity... casting doubt on lower empirical estimates), and so failed to critically examine if their results might have errors.

As you mention, much of this has been discussed before, including the principle that small natural variations can't trigger a very long term upward trend in temperature and ocean heat uptake in the absence of a climate sensitivity value that is astronomically high (Swanson and Tsonis have made essentially the same point about long term trends).

I personally think it is very likely because he used a climate sensitivity estimate that was high by a factor of 2 or more.

This was very likely because Hansen's models used a climate sensitivity that was two times too high.

Imposing a flat prior on an observable property, such as the climate feedback or transient climate response, is equivalent to imposing a highly skewed prior on the equilibrium climate sensitivity, and therefore results in narrower posterior likelihood ranges on the climate sensitivity that exclude very high sensitivities.

... In particular, it has proved extremely difficult to rule out very high values of climate sensitivity using observations (Gregory et al. 2002).»

Hansen and Sato argue that the probable range of climate sensitivity values is not as large as currently believed (unlikely to fall outside the range of 2 to 4 °C for doubled CO2)- both very high and very low values can effectively be ruled out using paleoclimate data.

For one, the non-linear relationship between warming and economic harm means that the most extreme damages would occur in very high - sensitivity cases (as Harvard economist Marty Weitzman puts it, «the sting is in the long tail» of climate sensitivity).

James: The fact that you believe that the high - end estimates of climate sensitivity are very unlikely is now a «Breaking...» story over in Wattsland: http://wattsupwiththat.com/2013/02/01/encouraging-admission-of-lower-climate-sensitivity-by-a-hockey-team-scientist I have submitted a comment there pointing out in essence that this story actually broke about 7 years ago.

Low sensitivity likely The very high complexity of IPCC Global Climate Models with Armstrong's findings infer that the IPCC's > 95 % confidence in > 50 % anthropogenic is «an illusion».

On the other hand, we probably underestimate the sensitivity at very high CO2 amounts, because our model (such as most climate models) does not change the total atmospheric mass as the CO2 amount varies.

The only way that I can see that the climate could be as warm as today (as «Skeptics» claim) is if climate sensitivity (CS) was very high, but the «skeptics» claim that CS is very low — a clear contradiction.

Skeptics have argued for quite some time that climate models assume too high of a sensitivity of temperature to CO2 — in other words, while most of us agree that Co2 increases can affect temperatures somewhat, the models assume temperature to be very sensitive to CO2, in large part because the models assume that the world's climate is dominated by positive feedback.

Equilibrium climate sensitivity is likely in the range 1.5 °C to 4.5 °C (high confidence), extremely unlikely less than 1 °C (high confidence), and very unlikely greater than 6 °C (medium confidence).