Decadal global temperature variability increases strongly with climate sensitivity

Nijsse, Femke J. M. M.; Cox, Peter M.; Huntingford, Chris; Williamson, Mark S.

doi:10.1038/s41558-019-0527-4

Cited by 41 publications

(57 citation statements)

References 25 publications

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“…Global climate models, such as the Earth system models that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5), reproduce the long-term trend in global ocean heat content over the last 50 years when uncertainties of observation-based estimates and internally generated natural variability are taken into account (Frölicher and Paynter, 2015;Cheng et al, 2019). Modelling studies agree on the sign of oceanic O 2 changes but likely underestimate the magnitude of loss (Bopp et al, 2013;Cocco et al, 2013;Oschlies et al, 2017). In particular in the tropical regions, models are not able to reproduce observed O 2 decrease in equatorial low-oxygen zones (Stramma et al, 2008;Cocco et al, 2013;Cabré et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Is deoxygenation detectable before warming in the thermocline?

et al. 2020

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Abstract. Anthropogenic greenhouse gas emissions cause ocean warming and oxygen depletion, with adverse impacts on marine organisms and ecosystems. Warming is one of the main indicators of anthropogenic climate change, but, in the thermocline, changes in oxygen and other biogeochemical tracers may emerge from the bounds of natural variability prior to warming. Here, we assess the time of emergence (ToE) of anthropogenic change in thermocline temperature and thermocline oxygen within an ensemble of Earth system model simulations from the fifth phase of the Coupled Model Intercomparison Project. Changes in temperature typically emerge from internal variability prior to changes in oxygen. However, in about a third (35±11 %) of the global thermocline deoxygenation emerges prior to warming. In these regions, both reduced ventilation and reduced solubility add to the oxygen decline. In addition, reduced ventilation slows the propagation of anthropogenic warming from the surface into the ocean interior, further contributing to the delayed emergence of warming compared to deoxygenation. Magnitudes of internal variability and of anthropogenic change, which determine ToE, vary considerably among models leading to model–model differences in ToE. We introduce a new metric, relative ToE, to facilitate the multi-model assessment of ToE. This reduces the inter-model spread compared to the traditionally evaluated absolute ToE. Our results underline the importance of an ocean biogeochemical observing system and that the detection of anthropogenic impacts becomes more likely when using multi-tracer observations.

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Section: Introductionmentioning

confidence: 99%

Is deoxygenation detectable before warming in the thermocline?

et al. 2020

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“…Starred models had full model output available and are the ones included in the emergent constraint. Values for CMIP5 are from (Flato et al, 2013), and model selection the same as in (Nijsse et al, 2019). Warming ∆T is calculated as the difference in smoothed GMSAT between two periods, typically the years 1970-1980 and 2008-2018.…”

Section: Methodsmentioning

confidence: 99%

An emergent constraint on Transient Climate Response from simulated historical warming in CMIP6 models

Nijsse

Cox

Williamson

2020

Preprint

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Abstract. The transient climate response (TCR) is the metric of temperature sensitivity that is most relevant to warming in the next few decades, and contributes the biggest uncertainty to estimates of the carbon budgets consistent with the Paris targets (Arora et al., 2019). In the IPCC 5th Assessment Report (AR5), the stated likely range of TCR was given as 1.0 to 2.5 K, with a central estimate which was broadly consistent with the ensemble mean of the CMIP5 Earth System Models (ESMs) available at the time (1.8 ± 0.4 K). Many of the latest CMIP6 ESMs have larger climate sensitivities, with 6 of 23 models having TCR values above 2.5 K, and an ensemble mean TCR of 2.1 ± 0.4 K. On the face of it, these latest ESM results suggest that the IPCC likely range of TCR may need revising upwards, which would cast further doubt on the feasibility of the Paris targets. Here we show that rather than increasing the uncertainty in climate sensitivity, the CMIP6 models help to further constrain the likely range of TCR to 1.5–2.2 K, with a central estimate of 1.82 K. We reach this conclusion through an emergent constraint approach which relates the value of TCR to the global warming from 1970 onwards. We confirm a consistent emergent constraint on TCR when we apply the same method to CMIP5 models (Jiménez-de-la Cuesta and Mauritsen, 2019). Our emergent constraint on TCR benefits from both the large range of TCR values across the CMIP6 models, and also from the extension of the historical simulations into a period when the uncertain changes in aerosol forcing have had a far less significant impact on the trend in global warming.

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“…We thank Matti Morzfeld and anonymous reviewer for thoughtful comments. We also thank Tushar Mittal for bring the study of Nijsse et al (2019) to our attention.…”

Section: Acknowledgmentsmentioning

confidence: 98%

“…Nijsse et al () derived a closed‐form expression for

σ_{b}

in the context of a related problem in climate science. We defer the details to a supporting information and simply state the general form of the standard deviation

σ_{b} = \sqrt{24 γ D f false(γ w false)}

where

f

is a known function of

γ w

(or, equivalently

w false/ τ_{γ}

).…”

Section: Variability Of the Trendmentioning

confidence: 99%

Variability of Millennial‐Scale Trends in the Geomagnetic Axial Dipole

Buffett

Davis

Avery

2019

Geophysical Research Letters

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The historical trend in the axial dipole is sufficient to reverse the field in less than 2 kyr.Assessing the prospect of an imminent polarity reversal depends on the probability of sustaining the historical trend for long enough to produce a reversal. We use a stochastic model to predict the variability of trends for arbitrary time windows. Our predictions agree well with the trends computed from paleomagnetic models. Applying these predictions to the historical record shows that the current trend is likely due to natural variability. Furthermore, an extrapolation of the current trend for the next 1 to 2 kyr is highly unlikely. Instead, we compute the trend and time window needed to reverse the field with a specified probability. We find that the dipole could reverse in the next 20 kyr with a probability of 2%.

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Decadal global temperature variability increases strongly with climate sensitivity

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Cited by 41 publications

References 25 publications

Is deoxygenation detectable before warming in the thermocline?

Is deoxygenation detectable before warming in the thermocline?

An emergent constraint on Transient Climate Response from simulated historical warming in CMIP6 models

Variability of Millennial‐Scale Trends in the Geomagnetic Axial Dipole

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