A brief analysis based on multi-gas emission pathways and several climate
sensitivity uncertainty estimates», Avoiding dangerous climate change, in H.J. Schellnhuber et al. (eds.)
Using available climate
sensitivity uncertainty estimates (pdfs by Murphy et al., Gregory et al., Forest et al., Wigley & Raper, Knutti et al., etc...), the probability of overshooting 2 °C global mean temperature rise above pre-industrial levels for a stabilization at 550ppm CO2eq are between 70 % -99 %.
A brief analysis based on multi-gas emission pathways and several climate
sensitivity uncertainty estimates.
Not exact matches
95 % UI =
uncertainty interval around the cost and DALY
estimates, derived from multivariate
sensitivity analysis propagating
uncertainty around cost inputs, elasticity
estimates, relative risks of disease outcomes and the prevalence of alcohol consumption.
It tries to turn a major factor in the
uncertainty in climate
sensitivity estimates — the behavior of clouds — into a strength.
Indeed, the main quandary faced by climate scientists is how to
estimate climate
sensitivity from the Little Ice Age or Medieval Warm Period, at all, given the relative small forcings over the past 1000 years, and the substantial
uncertainties in both the forcings and the temperature changes.
Only a few
estimates account for
uncertainty in forcings other than from aerosols (e.g., Gregory et al., 2002a; Knutti et al., 2002, 2003); some other studies perform some
sensitivity testing to assess the effect of forcing
uncertainty not accounted for, for example, in natural forcing (e.g., Forest et al., 2006; see Table 9.1 for an overview).
(in general, whether for future projections or historical reconstructions or
estimates of climate
sensitivity, I tend to be sympathetic to arguments of more rather than less
uncertainty because I feel like in general, models and statistical approaches are not exhaustive and it is «plausible» that additional factors could lead to either higher or lower
estimates than seen with a single approach.
This
sensitivity estimate is not the last word on the subject, because of
uncertainties in the approximate formulae used to compute the terms in the energy balance, and neglect of possible effects of water vapor feedback on the surface budget.
Probabilistic
estimates of transient climate
sensitivity subject to
uncertainty in forcing and natural variability.
This is also a good recent presentation of the various
estimates of climate
sensitivity and of the amount of
uncertainty associated with them — found by doing a Google image search on the terms:
This is enough to matter, but it's no more scary than the
uncertainty in cloud feedbacks for example, and whether they could put us on the high end of typical climate
sensitivity estimates.
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.
Regarding ECS («equilibrium climate
sensitivity»), I think there are difficulties
estimating anything truly resembling a Charney - type ECS from data involving OHC uptake and forcing
estimates, because these
estimates are fraught with so many
uncertainties, and because the values that are calculated, even if accurate, bear an uncertain relationship to how the climate would behave at equilibrium.
Indeed, the main quandary faced by climate scientists is how to
estimate climate
sensitivity from the Little Ice Age or Medieval Warm Period, at all, given the relative small forcings over the past 1000 years, and the substantial
uncertainties in both the forcings and the temperature changes.
Here as with CO2
sensitivity, most of the
uncertainty is on the high - side of the best guess, but we are mainly concerned with the best
estimate.
Schneider, T., 2007:
Uncertainty in climate -
sensitivity estimates.
Sensitivity of the climate to carbon dioxide, and the level of
uncertainty in its value, is a key input into the economic models that drive cost - benefit analyses, including
estimates of the social cost of carbon.
Can you say if this work changes our understanding of the central
estimate or
uncertainty of climate
sensitivity?
It is well known that the ERFaero, the sum of direct aerosol forcing (ERFari) and ERFaci is by far the greatest source of
uncertainty when it comes to observationally based
estimates about the transient
sensitivity (TCR) and the expected warming in this century.
Using a global energy budget approach, this paper seeks to understand the implications for climate
sensitivity (both ECS and TCR) of the new
estimates of radiative forcing and
uncertainty therein given in AR5.
It is hoped that providing these 100 realisations in a form identical to the median
estimate will encourage users to explore the
sensitivity of their analysis to observational
uncertainty with little extra effort.
Yeah, they're keeping that a huge secret: Section 8.6.3.2 of AR4 is called «Clouds,» and contains the statement «cloud feedbacks remain the largest source of
uncertainty in climate
sensitivity estimates.»
Because of the many
uncertainties involved, any
estimate of climate
sensitivity comes with a range, a lower and upper limit within which the real value could reasonably lie.
«
uncertainty» (in the IPCC attribution of natural versus human - induced climate changes, IPCC's model - based climate
sensitivity estimates and the resulting IPCC projections of future climate) is arguably the defining issue in climate science today.
Lewis says that «CLARREO's contribution of more accurate and comprehensive data is likely to speed up the reduction in
uncertainty,» in
estimates of climate
sensitivity.
from the pdf: Using a global energy budget approach, this paper seeks to understand the implications for climate
sensitivity (both ECS and TCR) of the new
estimates of radiative forcing and
uncertainty therein given in AR5.
She said climate
sensitivity and
estimates of its
uncertainty were important to establishing the cost benefit of taking action to limit greenhouse gas emissions.
To the contrarian, it is just a matter of time before other
uncertainties will yield even lower
estimates of
sensitivity, until eventually it will fall to the point that it is nothing significant.
The bottom line is that spatial averaging of temperature data introduces yet another layer of
uncertainty into climate
sensitivity estimates.
The point is that using the IPCC's own
estimates of forcings and associated
uncertainties, the
estimated sensitivity PDF falls far below the «distribution» of
sensitivities diagnosed by GCM's.
Given current
uncertainties in representing convective precipitation microphysics and the current inability to find a clear obser - vational constraint that favors one version of the authors» model over the others, the implications of this ability to engineer climate
sensitivity need to be considered when
estimating the
uncertainty in climate projections.»
Nic invited me to coauthor this paper, and I was delighted to given my concerns about ignoring
uncertainties in external forcing in attribution arguments and climate
sensitivity estimates (which I discussed in the
Uncertainty Monster paper).
The
estimate of climate
sensitivity and its associated
uncertainty -LRB-!)
I again used the variance in our
estimate of climate
sensitivity as an indicator of
uncertainty — if you are unclear about what that means, refresh your memory here.
In context of the way climate
sensitivity is defined by the IPCC,
uncertainty in climate
sensitivity is decreasing as errors in previous observational
estimates are identified and eliminated and model
estimates seem to be converging more.
Climate science has been thrown into disarray by the hiatus, disagreement between climate model and instrumental
estimates of climate
sensitivity,
uncertainties in carbon uptake by plants, and diverging interpretations of ocean heating (in the face of a dearth of observations).
This bias may be explained by a misrepresentation of mixed - phase extratropical clouds, often pinpointed as playing a key role in driving global - cloud feedback and
uncertainties in climate
sensitivity estimates (e.g., Tan et.
Using 72 - day averages resulted in a
sensitivity ~ 1.0 C during the Pinatubo years, although there's a lot of noise and
uncertainty around all the
estimates.
It is worth noting that inferences of climate
sensitivity from energy budget
estimates suggest low ECS values, i.e., ~ 2 K, but their
uncertainty is so large that they can not exclude much higher ECS (Forster 2016).
The problem with
sensitivity estimates based on ancient data is the great
uncertainty of the input data (solar activity, land albedo, etc), which creates very fuzzy numbers.
These
uncertainties may partly explain the typically weak correlations found between paleoclimate indices and climate projections, and the difficulty in narrowing the spread in models» climate
sensitivity estimates from paleoclimate - based emergent constraints (Schmidt et.
and «no data or computer code appears to be archived in relation to the paper» and «the
sensitivity of Shindell's TCR
estimate to the aerosol forcing bias adjustment is such that the true
uncertainty of Shindell's TCR range must be huge — so large as to make his
estimate worthless» and the seemingly arbitrary to cherry picked climate models used in Shindell's analysis.
When they define
sensitivity or human contribution only with respect to their
estimated forcings, it is implied that these are correct, but we know that the
uncertainty with respect to clouds, aerosols, etc is large.
Changes in cloudiness in a warmer climate can be either a negative or positive feedback and the
uncertainty in this feedback is the major source of
uncertainty in the IPCC's
estimate of climate
sensitivity.
Gabi Hegerl did publish an
estimate of climate
sensitivity in 2006 based on a new proxy temperature reconstruction (only the last 700 years due to excessive
uncertainty in forcings before then), which was cited in AR4 (Ch 9 of WG1).
While climate contrarians like Richard Lindzen tend to treat the
uncertainties associated with clouds and aerosols incorrectly, as we noted in that post, they are correct that these
uncertainties preclude a precise
estimate of climate
sensitivity based solely on recent temperature changes and model simulations of those changes.
Energy budget
estimates of equilibrium climate
sensitivity (ECS) and transient climate response (TCR) are derived based on the best
estimates and
uncertainty ranges for forcing provided in the IPCC Fifth Assessment Scientific Report (AR5).
The wide range of
estimates of climate
sensitivity is attributable to
uncertainties about the magnitude of climate feedbacks (e.g., water vapor, clouds, and albedo).
Energy budget
estimates of equilibrium climate
sensitivity (ECS) and transient climate response (TCR) are derived using the comprehensive 1750 — 2011 time series and the
uncertainty ranges for forcing components provided in the Intergovernmental Panel on Climate Change Fifth Assessment Working Group I Report, along with its
estimates of heat accumulation in the climate system.