How Robust Are Trends in the Brewer–Dobson Circulation Derived from Observed Stratospheric Temperatures?

Abstract Most global circulation models and climate–chemistry models forced with increasing greenhouse gases predict a strengthening of the Brewer–Dobson circulation (BDC) in the twenty-first century, and some of them claim that such strengthening has already begun at the end of the twentieth century. However, observational evidence for such a trend remains inconclusive. The goal of this paper is to examine the evidence for observed trends in the stratospheric overturning circulation using a suite of currently available observational stratospheric temperature data. Trends are examined as “departures” from the global mean temperature, since such trends reflect the effects of dynamics and spatially inhomogeneous radiative forcing and are to first order independent of the direct radiative effects of increasing well-mixed greenhouse gas concentrations. The primary conclusion of the study is that temperature observations do not reveal statistically significant trends in the Brewer–Dobson circulation over the period from 1979 to the present, as covered by Microwave Sounding Unit and Stratospheric Sounding Unit temperatures. The estimated trends in the BDC are weak in all datasets and not statistically significant at the 95% confidence level. In many cases, different data products yield very different results, particularly when the trends are stratified by season. Implications for the interpretation of recent stratospheric climate change are discussed. The results illustrate the essential need to better constrain the accuracy of future stratospheric temperature datasets.

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A method for merging nadir-sounding climate records, with an application to the global-mean stratospheric temperature data sets from SSU and AMSU

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-10085-2015 ◽

2015 ◽

Vol 15 (7) ◽

pp. 10085-10122 ◽

Cited By ~ 2

Author(s):

C. McLandress ◽

T. G. Shepherd ◽

A. I. Jonsson ◽

T. von Clarmann ◽

B. Funke

Keyword(s):

Climate Model ◽

Michelson Interferometer ◽

Data Sets ◽

Climate Data ◽

Data Set ◽

Stratospheric Temperature ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

Climate Model Simulations ◽

Global Mean

Abstract. A method is proposed for merging different nadir-sounding climate data records using measurements from high resolution limb sounders to provide a transfer function between the different nadir measurements. The nadir-sounding records need not be overlapping so long as the limb-sounding record bridges between them. The method is applied to global mean stratospheric temperatures from the NOAA Climate Data Records based on the Stratospheric Sounding Unit (SSU) and the Advanced Microwave Sounding Unit-A (AMSU), extending the SSU record forward in time to yield a continuous data set from 1979 to present. SSU and AMSU are bridged using temperature measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), which is of high enough vertical resolution to accurately represent the weighting functions of both SSU and AMSU. For this application, a purely statistical approach is not viable since the different nadir channels are not sufficiently linearly independent, statistically speaking. The extended SSU global-mean data set is in good agreement with temperatures from the Microwave Limb Sounder (MLS) on the Aura satellite, with both exhibiting a cooling trend of ~ 0.6 ± 0.3 K decade−1 in the upper stratosphere from 2004–2012. The extended SSU data set also compares well with chemistry-climate model simulations over its entire record, including the contrast between the weak cooling seen over 1995–2004 compared with the large cooling seen in the period 1986–1995 of strong ozone depletion.

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The Stratospheric Changes Inferred from 10 Years of AIRS and AMSU-A Radiances

Journal of Climate ◽

10.1175/jcli-d-17-0037.1 ◽

2017 ◽

Vol 30 (15) ◽

pp. 6005-6016 ◽

Cited By ~ 6

Author(s):

Fang Pan ◽

Xianglei Huang ◽

Stephen S. Leroy ◽

Pu Lin ◽

L. Larrabee Strow ◽

...

Keyword(s):

Cooling Rate ◽

Lower Stratosphere ◽

Natural Variability ◽

Atmospheric Infrared Sounder ◽

Stratospheric Temperature ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

Microwave Radiances ◽

Global Mean

Global-mean radiances observed by the Atmospheric Infrared Sounder (AIRS) and the Advanced Microwave Sounding Unit A (AMSU-A) are analyzed from 2003 to 2012. The focus of this study is on channels sensitive to emission and absorption in the stratosphere. Optimal fingerprinting is used to obtain estimates of changes of stratospheric temperature in five vertical layers due to external forcing in the presence of natural variability. Natural variability is estimated using synthetic radiances based on the 500-yr GFDL CM3 and 240-yr HadGEM2-CC control runs. The results show a cooling rate of 0.65 ± 0.11 (2 σ) K decade−1 in the upper stratosphere above 6 hPa, approximately 0.46 ± 0.24 K decade−1 in two midstratospheric layers between 6 and 30 hPa, and 0.39 ± 0.32 K decade−1 in the lower stratosphere (30–60 hPa). The cooling rate in the lowest part of the stratosphere (60–100 hPa) is −0.014 ± 0.22 K decade−1, which is smallest among all five layers and statistically insignificant. The synergistic use of well-calibrated passive infrared and microwave radiances permits disambiguation of trends of carbon dioxide and stratospheric temperature, increases vertical resolution of detected stratospheric temperature trends, and effectively reduces uncertainties of estimated temperature trends.

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Estimates of Uncertainty in Predictions of Global Mean Surface Temperature

Journal of Climate ◽

10.1175/jcli4012.1 ◽

2007 ◽

Vol 20 (5) ◽

pp. 843-855 ◽

Cited By ~ 19

Author(s):

J. A. Kettleborough ◽

B. B. B. Booth ◽

P. A. Stott ◽

M. R. Allen

Keyword(s):

Twentieth Century ◽

Energy Balance ◽

Temperature Change ◽

Radiative Forcing ◽

Balance Model ◽

Future Climate Change ◽

Model Parameters ◽

Global Mean Temperature ◽

Mean Temperature ◽

Global Mean

Abstract A method for estimating uncertainty in future climate change is discussed in detail and applied to predictions of global mean temperature change. The method uses optimal fingerprinting to make estimates of uncertainty in model simulations of twentieth-century warming. These estimates are then projected forward in time using a linear, compact relationship between twentieth-century warming and twenty-first-century warming. This relationship is established from a large ensemble of energy balance models. By varying the energy balance model parameters an estimate is made of the error associated with using the linear relationship in forecasts of twentieth-century global mean temperature. Including this error has very little impact on the forecasts. There is a 50% chance that the global mean temperature change between 1995 and 2035 will be greater than 1.5 K for the Special Report on Emissions Scenarios (SRES) A1FI scenario. Under SRES B2 the same threshold is not exceeded until 2055. These results should be relatively robust to model developments for a given radiative forcing history.

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Impact of methane and black carbon mitigation on forcing and temperature: a multi-model scenario analysis

Climatic Change ◽

10.1007/s10584-020-02794-3 ◽

2020 ◽

Vol 163 (3) ◽

pp. 1427-1442 ◽

Cited By ~ 3

Author(s):

Steven J Smith ◽

Jean Chateau ◽

Kalyn Dorheim ◽

Laurent Drouet ◽

Olivier Durand-Lasserve ◽

...

Keyword(s):

Black Carbon ◽

Radiative Forcing ◽

Climate Model ◽

Economic Structure ◽

Time Frame ◽

Focused Attention ◽

Carbon Mitigation ◽

Global Mean Temperature ◽

Model Parameter Uncertainty ◽

Global Mean

AbstractThe relatively short atmospheric lifetimes of methane (CH4) and black carbon (BC) have focused attention on the potential for reducing anthropogenic climate change by reducing Short-Lived Climate Forcer (SLCF) emissions. This paper examines radiative forcing and global mean temperature results from the Energy Modeling Forum (EMF)-30 multi-model suite of scenarios addressing CH4 and BC mitigation, the two major short-lived climate forcers. Central estimates of temperature reductions in 2040 from an idealized scenario focused on reductions in methane and black carbon emissions ranged from 0.18–0.26 °C across the nine participating models. Reductions in methane emissions drive 60% or more of these temperature reductions by 2040, although the methane impact also depends on auxiliary reductions that depend on the economic structure of the model. Climate model parameter uncertainty has a large impact on results, with SLCF reductions resulting in as much as 0.3–0.7 °C by 2040. We find that the substantial overlap between a SLCF-focused policy and a stringent and comprehensive climate policy that reduces greenhouse gas emissions means that additional SLCF emission reductions result in, at most, a small additional benefit of ~ 0.1 °C in the 2030–2040 time frame.

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Future Global Meteorological Drought Hot Spots: A Study Based on CORDEX Data

Journal of Climate ◽

10.1175/jcli-d-19-0084.1 ◽

2020 ◽

Vol 33 (9) ◽

pp. 3635-3661 ◽

Cited By ~ 22

Author(s):

Jonathan Spinoni ◽

Paulo Barbosa ◽

Edoardo Bucchignani ◽

John Cassano ◽

Tereza Cavazos ◽

...

Keyword(s):

Hot Spots ◽

Regional Climate ◽

Standardized Precipitation Index ◽

Meteorological Drought ◽

First Century ◽

Horn Of Africa ◽

Global Circulation ◽

Global Circulation Models ◽

The Standardized Precipitation Index ◽

Meteorological Droughts

AbstractTwo questions motivated this study: 1) Will meteorological droughts become more frequent and severe during the twenty-first century? 2) Given the projected global temperature rise, to what extent does the inclusion of temperature (in addition to precipitation) in drought indicators play a role in future meteorological droughts? To answer, we analyzed the changes in drought frequency, severity, and historically undocumented extreme droughts over 1981–2100, using the standardized precipitation index (SPI; including precipitation only) and standardized precipitation-evapotranspiration index (SPEI; indirectly including temperature), and under two representative concentration pathways (RCP4.5 and RCP8.5). As input data, we employed 103 high-resolution (0.44°) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), based on a combination of 16 global circulation models (GCMs) and 20 regional circulation models (RCMs). This is the first study on global drought projections including RCMs based on such a large ensemble of RCMs. Based on precipitation only, ~15% of the global land is likely to experience more frequent and severe droughts during 2071–2100 versus 1981–2010 for both scenarios. This increase is larger (~47% under RCP4.5, ~49% under RCP8.5) when precipitation and temperature are used. Both SPI and SPEI project more frequent and severe droughts, especially under RCP8.5, over southern South America, the Mediterranean region, southern Africa, southeastern China, Japan, and southern Australia. A decrease in drought is projected for high latitudes in Northern Hemisphere and Southeast Asia. If temperature is included, drought characteristics are projected to increase over North America, Amazonia, central Europe and Asia, the Horn of Africa, India, and central Australia; if only precipitation is considered, they are found to decrease over those areas.

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Robustness of Tropospheric Temperature Trends from MSU Channels 2 and 4

Journal of Climate ◽

10.1175/jcli3866.1 ◽

2006 ◽

Vol 19 (17) ◽

pp. 4234-4242 ◽

Cited By ~ 22

Author(s):

Celeste M. Johanson ◽

Qiang Fu

Keyword(s):

Training Dataset ◽

Retrieval Algorithm ◽

Tropospheric Temperature ◽

Temperature Trends ◽

Combining Data ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

The Mean ◽

Stratospheric Cooling ◽

Global Mean

Abstract Tropospheric temperature trends based on Microwave Sounding Unit (MSU) channel 2 data are susceptible to contamination from strong stratospheric cooling. Recently, Fu et al. devised a method of removing the stratospheric contamination by linearly combining data from MSU channels 2 and 4. In this study the sensitivity of the weights of the two channels in the retrieval algorithm for the tropospheric temperatures to the choice of period of record used in the analysis and to the choice of training dataset is examined. The weights derived using monthly temperature anomalies are within about 10% of those obtained by Fu et al. irrespective of the choice of analysis period or training dataset. The trend errors in the retrieved global-mean tropospheric temperatures tested using two independent radiosonde datasets are less than about 0.01 K decade−1 for all time periods of 25 yr or longer with different starting and ending years during 1958–2004. It is found that the retrievals are more robust if they are interpreted in terms of the layer-mean temperature for the entire troposphere, rather than the mean of the 850–300-hPa layer. Because large spurious jumps remain in the reanalyses, especially prior to 1979, one should be cautious when using them as training datasets and in testing the trend errors.

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A method for merging nadir-sounding climate records, with an application to the global-mean stratospheric temperature data sets from SSU and AMSU

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-9271-2015 ◽

2015 ◽

Vol 15 (16) ◽

pp. 9271-9284 ◽

Cited By ~ 13

Author(s):

C. McLandress ◽

T. G. Shepherd ◽

A. I. Jonsson ◽

T. von Clarmann ◽

B. Funke

Keyword(s):

Michelson Interferometer ◽

Data Sets ◽

Climate Data ◽

Data Set ◽

Linear Temperature ◽

Temperature Changes ◽

Stratospheric Temperature ◽

Temperature Trends ◽

Microwave Sounding ◽

Global Mean

Abstract. A method is proposed for merging different nadir-sounding climate data records using measurements from high-resolution limb sounders to provide a transfer function between the different nadir measurements. The two nadir-sounding records need not be overlapping so long as the limb-sounding record bridges between them. The method is applied to global-mean stratospheric temperatures from the NOAA Climate Data Records based on the Stratospheric Sounding Unit (SSU) and the Advanced Microwave Sounding Unit-A (AMSU), extending the SSU record forward in time to yield a continuous data set from 1979 to present, and providing a simple framework for extending the SSU record into the future using AMSU. SSU and AMSU are bridged using temperature measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), which is of high enough vertical resolution to accurately represent the weighting functions of both SSU and AMSU. For this application, a purely statistical approach is not viable since the different nadir channels are not sufficiently linearly independent, statistically speaking. The near-global-mean linear temperature trends for extended SSU for 1980–2012 are −0.63 ± 0.13, −0.71 ± 0.15 and −0.80 ± 0.17 K decade−1 (95 % confidence) for channels 1, 2 and 3, respectively. The extended SSU temperature changes are in good agreement with those from the Microwave Limb Sounder (MLS) on the Aura satellite, with both exhibiting a cooling trend of ~ 0.6 ± 0.3 K decade−1 in the upper stratosphere from 2004 to 2012. The extended SSU record is found to be in agreement with high-top coupled atmosphere–ocean models over the 1980–2012 period, including the continued cooling over the first decade of the 21st century.

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A Re-evaluation of Climate Sensitivity

10.20944/preprints202105.0583.v1 ◽

2021 ◽

Author(s):

Ian Harold Wilson

Keyword(s):

Climate Sensitivity ◽

Radiative Forcing ◽

Co2 Concentration ◽

Systematic Errors ◽

Short Term ◽

The Past ◽

Global Mean Temperature ◽

Recent Climate ◽

Global Mean ◽

Paleoclimate Data

Equilibrium climate sensitivity (ECS) is the change in global mean temperature expected to result from doubling atmospheric CO2 concentration from pre-industrial levels. Extensive research during the past 40 years has not reduced the uncertainty associated with ECS. Sherwood et al. [1] applied Bayesian statistics to evidence from climate-process physics, historical observations and earlier proxies to reduce the range of ECS from 1.5 – 4.5 K to 2.6 – 4.1 K. This paper examines their methods and many of the assumptions they made. It also evaluates two additional periods in the Holocene to show that factors other than CO2 drove recent climate change. It identifies potential systematic errors resulting from adding non-equilibrium short-term adjustments to the radiative forcing of greenhouse gases and from underestimating the effects of solar irradiance, ocean currents and aerosols. These factors have resulted in estimates of the forcing by CO2 that far exceed the apparent effects in paleoclimate data.

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Estimating trends in the global mean temperature record

Advances in Statistical Climatology Meteorology and Oceanography ◽

10.5194/ascmo-3-33-2017 ◽

2017 ◽

Vol 3 (1) ◽

pp. 33-53 ◽

Cited By ~ 13

Author(s):

Andrew Poppick ◽

Elisabeth J. Moyer ◽

Michael L. Stein

Keyword(s):

Radiative Forcing ◽

Temporal Correlation ◽

Internal Variability ◽

Historical Record ◽

Temperature Record ◽

Empirical Methods ◽

Global Mean Temperature ◽

Data Record ◽

Historical Temperature ◽

Global Mean

Abstract. Given uncertainties in physical theory and numerical climate simulations, the historical temperature record is often used as a source of empirical information about climate change. Many historical trend analyses appear to de-emphasize physical and statistical assumptions: examples include regression models that treat time rather than radiative forcing as the relevant covariate, and time series methods that account for internal variability in nonparametric rather than parametric ways. However, given a limited data record and the presence of internal variability, estimating radiatively forced temperature trends in the historical record necessarily requires some assumptions. Ostensibly empirical methods can also involve an inherent conflict in assumptions: they require data records that are short enough for naive trend models to be applicable, but long enough for long-timescale internal variability to be accounted for. In the context of global mean temperatures, empirical methods that appear to de-emphasize assumptions can therefore produce misleading inferences, because the trend over the twentieth century is complex and the scale of temporal correlation is long relative to the length of the data record. We illustrate here how a simple but physically motivated trend model can provide better-fitting and more broadly applicable trend estimates and can allow for a wider array of questions to be addressed. In particular, the model allows one to distinguish, within a single statistical framework, between uncertainties in the shorter-term vs. longer-term response to radiative forcing, with implications not only on historical trends but also on uncertainties in future projections. We also investigate the consequence on inferred uncertainties of the choice of a statistical description of internal variability. While nonparametric methods may seem to avoid making explicit assumptions, we demonstrate how even misspecified parametric statistical methods, if attuned to the important characteristics of internal variability, can result in more accurate uncertainty statements about trends.

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Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska

Quaternary Research ◽

10.1016/s0033-5894(03)00040-1 ◽

2003 ◽

Vol 59 (3) ◽

pp. 411-419 ◽

Cited By ~ 94

Author(s):

Helen M. Roberts ◽

Daniel R. Muhs ◽

Ann G. Wintle ◽

Geoff A. T. Duller ◽

E. Arthur Bettis

Keyword(s):

North America ◽

Radiative Forcing ◽

Luminescence Dating ◽

Accumulation Rates ◽

Last Glacial ◽

Global Circulation ◽

Global Circulation Models ◽

Mass Accumulation Rates ◽

Mass Accumulation ◽

Dust Accumulation

AbstractA high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35–50 μm quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil’s Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr—much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values.

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