scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 2: A pseudo-proxy study addressing the amplitude of solar forcing

2012 ◽  
Vol 8 (4) ◽  
pp. 1355-1365 ◽  
Author(s):  
A. Hind ◽  
A. Moberg ◽  
R. Sundberg
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Signal To Noise Ratio ◽  
Noise Levels ◽  
Solar Forcing ◽  
Max Planck ◽  
Statistical Framework ◽  
Spatial Coverage ◽  
Climate Model Simulations ◽  
Instrumental Records

Abstract. The statistical framework of Part 1 (Sundberg et al., 2012), for comparing ensemble simulation surface temperature output with temperature proxy and instrumental records, is implemented in a pseudo-proxy experiment. A set of previously published millennial forced simulations (Max Planck Institute – COSMOS), including both "low" and "high" solar radiative forcing histories together with other important forcings, was used to define "true" target temperatures as well as pseudo-proxy and pseudo-instrumental series. In a global land-only experiment, using annual mean temperatures at a 30-yr time resolution with realistic proxy noise levels, it was found that the low and high solar full-forcing simulations could be distinguished. In an additional experiment, where pseudo-proxies were created to reflect a current set of proxy locations and noise levels, the low and high solar forcing simulations could only be distinguished when the latter served as targets. To improve detectability of the low solar simulations, increasing the signal-to-noise ratio in local temperature proxies was more efficient than increasing the spatial coverage of the proxy network. The experiences gained here will be of guidance when these methods are applied to real proxy and instrumental data, for example when the aim is to distinguish which of the alternative solar forcing histories is most compatible with the observed/reconstructed climate.

scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 3: Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing

2014 ◽  
Vol 10 (3) ◽  
pp. 2627-2683
Author(s):  
A. Moberg ◽  
R. Sundberg ◽  
H. Grudd ◽  
A. Hind
Keyword(s):  
Tree Ring ◽  
Large Amplitude ◽  
Small Amplitude ◽  
Climate Model ◽  
Last Millennium ◽  
Solar Forcing ◽  
Proxy Data ◽  
Statistical Framework ◽  
Tree Ring Data ◽  
Climate Model Simulations

Abstract. Practical issues arise when applying a statistical framework for unbiased ranking of alternative forced climate model simulations by comparison with climate observations from instrumental and proxy data (Part 1 in this series). Given a set of model and observational data, several decisions need to be made; e.g. concerning the region that each proxy series represents, the weighting of different regions, and the time resolution to use in the analysis. Objective selection criteria cannot be made here, but we argue to study how sensitive the results are to the choices made. The framework is improved by the relaxation of two assumptions; to allow autocorrelation in the statistical model for simulated climate variability, and to enable direct comparison of alternative simulations to test if any of them fit the observations significantly better. The extended framework is applied to a set of simulations driven with forcings for the pre-industrial period 1000–1849 CE and fifteen tree-ring based temperature proxy series. Simulations run with only one external forcing (land-use, volcanic, small-amplitude solar, or large-amplitude solar), do not significantly capture the variability in the tree-ring data – although the simulation with volcanic forcing does so for some experiment settings. When all forcings are combined (using either the small- or large-amplitude solar forcing) including also orbital, greenhouse-gas and non-volcanic aerosol forcing, and additionally used to produce small simulation ensembles starting from slightly different initial ocean conditions, the resulting simulations are highly capable of capturing some observed variability. Nevertheless, for some choices in the experiment design, they are not significantly closer to the observations than when unforced simulations are used, due to highly variable results between regions. It is also not possible to tell whether the small-amplitude or large-amplitude solar forcing causes the multiple-forcing simulations to be closer to the reconstructed temperature variability. This suggests that proxy data from more regions and proxy types, or representing larger regions and other seasons, are needed for more conclusive results from model-data comparisons in the last millennium.

scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 3: Practical considerations, relaxed assumptions, and using tree-ring data to address the amplitude of solar forcing

2015 ◽  
Vol 11 (3) ◽  
pp. 425-448 ◽  
Author(s):  
A. Moberg ◽  
R. Sundberg ◽  
H. Grudd ◽  
A. Hind
Keyword(s):  
Tree Ring ◽  
Large Amplitude ◽  
Small Amplitude ◽  
Climate Model ◽  
Last Millennium ◽  
Solar Forcing ◽  
Proxy Data ◽  
Statistical Framework ◽  
Tree Ring Data ◽  
Climate Model Simulations

Abstract. A statistical framework for evaluation of climate model simulations by comparison with climate observations from instrumental and proxy data (part 1 in this series) is improved by the relaxation of two assumptions. This allows autocorrelation in the statistical model for simulated internal climate variability and enables direct comparison of two alternative forced simulations to test whether one fits the observations significantly better than the other. The extended framework is applied to a set of simulations driven with forcings for the pre-industrial period 1000–1849 CE and 15 tree-ring-based temperature proxy series. Simulations run with only one external forcing (land use, volcanic, small-amplitude solar, or large-amplitude solar) do not significantly capture the variability in the tree-ring data – although the simulation with volcanic forcing does so for some experiment settings. When all forcings are combined (using either the small- or large-amplitude solar forcing), including also orbital, greenhouse-gas and non-volcanic aerosol forcing, and additionally used to produce small simulation ensembles starting from slightly different initial ocean conditions, the resulting simulations are highly capable of capturing some observed variability. Nevertheless, for some choices in the experiment design, they are not significantly closer to the observations than when unforced simulations are used, due to highly variable results between regions. It is also not possible to tell whether the small-amplitude or large-amplitude solar forcing causes the multiple-forcing simulations to be closer to the reconstructed temperature variability. Proxy data from more regions and of more types, or representing larger regions and complementary seasons, are apparently needed for more conclusive results from model–data comparisons in the last millennium.

scholarly journals Statistical framework for evaluation of climate model simulations by use of climate proxy data from the last millennium – Part 1: Theory

2012 ◽  
Vol 8 (4) ◽  
pp. 1339-1353 ◽  
Author(s):  
R. Sundberg ◽  
A. Moberg ◽  
A. Hind
Keyword(s):  
Climate Model ◽  
Distance Measure ◽  
Last Millennium ◽  
Proxy Data ◽  
Simulation Data ◽  
Model Simulations ◽  
Climate Proxy ◽  
Statistical Framework ◽  
Climate Model Simulations ◽  
Instrumental Records

Abstract. A statistical framework for comparing the output of ensemble simulations from global climate models with networks of climate proxy and instrumental records has been developed, focusing on near-surface temperatures for the last millennium. This framework includes the formulation of a joint statistical model for proxy data, instrumental data and simulation data, which is used to optimize a quadratic distance measure for ranking climate model simulations. An essential underlying assumption is that the simulations and the proxy/instrumental series have a shared component of variability that is due to temporal changes in external forcing, such as volcanic aerosol load, solar irradiance or greenhouse gas concentrations. Two statistical tests have been formulated. Firstly, a preliminary test establishes whether a significant temporal correlation exists between instrumental/proxy and simulation data. Secondly, the distance measure is expressed in the form of a test statistic of whether a forced simulation is closer to the instrumental/proxy series than unforced simulations. The proposed framework allows any number of proxy locations to be used jointly, with different seasons, record lengths and statistical precision. The goal is to objectively rank several competing climate model simulations (e.g. with alternative model parameterizations or alternative forcing histories) by means of their goodness of fit to the unobservable true past climate variations, as estimated from noisy proxy data and instrumental observations.

scholarly journals Anthropogenic forcing and response yield observed positive trend in Earth’s energy imbalance

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shiv Priyam Raghuraman ◽  
David Paynter ◽  
V. Ramaswamy
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Solar Spectrum ◽  
Internal Variability ◽  
Satellite Observations ◽  
Positive Trend ◽  
Energy Imbalance ◽  
Model Simulations ◽  
Heat Uptake ◽  
Climate Model Simulations

AbstractThe observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. Satellite observations (2001–2020) reveal a significant positive globally-averaged TEEI of 0.38 ± 0.24 Wm−2decade−1, but the contributing drivers have yet to be understood. Using climate model simulations, we show that it is exceptionally unlikely (<1% probability) that this trend can be explained by internal variability. Instead, TEEI is achieved only upon accounting for the increase in anthropogenic radiative forcing and the associated climate response. TEEI is driven by a large decrease in reflected solar radiation and a small increase in emitted infrared radiation. This is because recent changes in forcing and feedbacks are additive in the solar spectrum, while being nearly offset by each other in the infrared. We conclude that the satellite record provides clear evidence of a human-influenced climate system.

scholarly journals Evaluating Climate Model Simulations of the Radiative Forcing and Radiative Response at Earth’s Surface

2019 ◽  
Vol 32 (13) ◽  
pp. 4089-4102 ◽  
Author(s):  
Ryan J. Kramer ◽  
Brian J. Soden ◽  
Angeline G. Pendergrass
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Hydrological Cycle ◽  
Global Climate ◽  
Global Climate Models ◽  
Lapse Rate ◽  
Radiation Budget ◽  
Model Simulations ◽  
Climate Model Simulations

Abstract We analyze the radiative forcing and radiative response at Earth’s surface, where perturbations in the radiation budget regulate the atmospheric hydrological cycle. By applying a radiative kernel-regression technique to CMIP5 climate model simulations where CO2 is instantaneously quadrupled, we evaluate the intermodel spread in surface instantaneous radiative forcing, radiative adjustments to this forcing, and radiative responses to surface warming. The cloud radiative adjustment to CO2 forcing and the temperature-mediated cloud radiative response exhibit significant intermodel spread. In contrast to its counterpart at the top of the atmosphere, the temperature-mediated cloud radiative response at the surface is found to be positive in some models and negative in others. Also, the compensation between the temperature-mediated lapse rate and water vapor radiative responses found in top-of-atmosphere calculations is not present for surface radiative flux changes. Instantaneous radiative forcing at the surface is rarely reported for model simulations; as a result, intermodel differences have not previously been evaluated in global climate models. We demonstrate that the instantaneous radiative forcing is the largest contributor to intermodel spread in effective radiative forcing at the surface. We also find evidence of differences in radiative parameterizations in current models and argue that this is a significant, but largely overlooked, source of bias in climate change simulations.

scholarly journals Teleconnections and relationship between ENSO and SAM in reconstructions and models over the past millennium

2019 ◽  
Author(s):  
Christoph Dätwyler ◽  
Martin Grosjean ◽  
Nathan J. Steiger ◽  
Raphael Neukom
Keyword(s):  
Climate Model ◽  
Southern Oscillation ◽  
Negative Temperature ◽  
Internal Variability ◽  
Southern Annular Mode ◽  
Teleconnection Patterns ◽  
Modes Of Variability ◽  
Proxy Records ◽  
Climate Model Simulations ◽  
Instrumental Records

Abstract. The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Due to the temporally very limited instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability and its stability over time. Here, we use proxy-based reconstructions and climate model simulations to quantify changes in tropical-extratropical SH teleconnections as represented by the correlation between the ENSO and SAM indices. Reconstructions indicate mostly negative correlations back to around 1400 CE confirming the pattern seen in the instrumental record over the last few decades. An ensemble of last millennium simulations of the model CESM1 confirms this pattern with very stable ensemble mean correlations around −0.3. Individual forced simulations, the pre-industrial control run and the proxy-based reconstructions indicate intermittent periods of positive correlations and particularly strong negative correlations. The fluctuations of the ENSO-SAM correlations are not significantly related to solar nor volcanic forcing in both proxy and model data, indicating that they are driven by internal variability in the climate system. Pseudoproxy experiments indicate that the currently available proxy records are able to reproduce the tropical-extratropical teleconnection patterns back to around 1600 CE. We analyse the spatial temperature and sea level pressure patterns during periods of positive and particularly strong negative teleconnections in the CESM model. Results indicate no consistent pattern during periods where the ENSO-SAM teleconnection changes its sign. However, periods of very strong negative SH teleconnections are associated with negative temperature anomalies across large fractions of the extra-tropical Pacific and a strengthening of the Aleutian Low.

Resolving the differences in the simulated and reconstructed climate response to volcanism over the last millennium

2020 ◽  
Author(s):  
Feng Zhu ◽  
Julien Emile-Geay ◽  
Greg Hakim ◽  
Jonathan King ◽  
Kevin Anchukaitis
Keyword(s):  
Tree Ring ◽  
Radiative Forcing ◽  
Natural Experiment ◽  
Climate Model ◽  
Simulated Data ◽  
Growing Season ◽  
Explosive Volcanism ◽  
Last Millennium ◽  
Climate Response ◽  
Climate Model Simulations

&lt;p&gt;Explosive volcanism imposes impulse-like radiative forcing on the climate system, providing a natural experiment to study the climate response to perturbation. Previous studies have identified disagreements between paleoclimate reconstructions and climate model simulations (GCMs) with respect to the magnitude and recovery from volcanic cooling, questioning the fidelity of GCMs, reconstructions, or both. Using the paleoenvironmental data assimilation framework of the Last Millennium Reanalysis, this study investigates the causes of the disagreements, using both real and simulated data. We demonstrate that the disagreement may be resolved by assimilating tree-ring density records only, by targeting growing-season temperature instead of annual temperature, and by performing the comparison at proxy locales. Our work suggests that discrepancies between paleoclimate models and data can be largely resolved by accounting for these features of tree-ring proxy networks.&lt;/p&gt;

scholarly journals Walker circulation response to extratropical radiative forcing

2020 ◽  
Vol 6 (47) ◽  
pp. eabd3021
Author(s):  
Sarah M. Kang ◽  
Shang-Ping Xie ◽  
Yechul Shin ◽  
Hanjun Kim ◽  
Yen-Ting Hwang ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Radiative Forcing ◽  
Climate Model ◽  
Walker Circulation ◽  
Coupled System ◽  
Subsurface Water ◽  
Eastern Equatorial Pacific ◽  
Global Impacts ◽  
Climate Model Simulations ◽  
The Walker Circulation

Walker circulation variability and associated zonal shifts in the heating of the tropical atmosphere have far-reaching global impacts well into high latitudes. Yet the reversed high latitude–to–Walker circulation teleconnection is not fully understood. Here, we reveal the dynamical pathways of this teleconnection across different components of the climate system using a hierarchy of climate model simulations. In the fully coupled system with ocean circulation adjustments, the Walker circulation strengthens in response to extratropical radiative cooling of either hemisphere, associated with the upwelling of colder subsurface water in the eastern equatorial Pacific. By contrast, in the absence of ocean circulation adjustments, the Walker circulation response is sensitive to the forcing hemisphere, due to the blocking effect of the northward-displaced climatological intertropical convergence zone and shortwave cloud radiative effects. Our study implies that energy biases in the extratropics can cause pronounced changes of tropical climate patterns.

scholarly journals Weighting climate model projections using observational constraints

2015 ◽  
Vol 373 (2054) ◽  
pp. 20140425 ◽  
Author(s):  
Nathan P. Gillett
Keyword(s):  
Climate Change ◽  
Radiative Forcing ◽  
Climate Model ◽  
Historical Period ◽  
Intergovernmental Panel ◽  
Transient Climate Response ◽  
Detection And Attribution ◽  
Future Warming ◽  
Near Term ◽  
Climate Model Simulations

Projected climate change integrates the net response to multiple climate feedbacks. Whereas existing long-term climate change projections are typically based on unweighted individual climate model simulations, as observed climate change intensifies it is increasingly becoming possible to constrain the net response to feedbacks and hence projected warming directly from observed climate change. One approach scales simulated future warming based on a fit to observations over the historical period, but this approach is only accurate for near-term projections and for scenarios of continuously increasing radiative forcing. For this reason, the recent Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) included such observationally constrained projections in its assessment of warming to 2035, but used raw model projections of longer term warming to 2100. Here a simple approach to weighting model projections based on an observational constraint is proposed which does not assume a linear relationship between past and future changes. This approach is used to weight model projections of warming in 2081–2100 relative to 1986–2005 under the Representative Concentration Pathway 4.5 forcing scenario, based on an observationally constrained estimate of the Transient Climate Response derived from a detection and attribution analysis. The resulting observationally constrained 5–95% warming range of 0.8–2.5 K is somewhat lower than the unweighted range of 1.1–2.6 K reported in the IPCC AR5.

scholarly journals Polar amplification of Pliocene climate by elevated trace gas radiative forcing

2020 ◽  
Vol 117 (38) ◽  
pp. 23401-23407
Author(s):  
Peter O. Hopcroft ◽  
Gilles Ramstein ◽  
Thomas A. M. Pugh ◽  
Stephen J. Hunter ◽  
Fabiola Murguia-Flores ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Trace Gas ◽  
Geological Evidence ◽  
Model Simulations ◽  
Climate Simulations ◽  
Climate Model Simulations ◽  
Near Future ◽  
Middle Pliocene

Warm periods in Earth’s history offer opportunities to understand the dynamics of the Earth system under conditions that are similar to those expected in the near future. The Middle Pliocene warm period (MPWP), from 3.3 to 3.0 My B.P, is the most recent time when atmospheric CO2levels were as high as today. However, climate model simulations of the Pliocene underestimate high-latitude warming that has been reconstructed from fossil pollen samples and other geological archives. One possible reason for this is that enhanced non-CO2trace gas radiative forcing during the Pliocene, including from methane (CH4), has not been included in modeling. We use a suite of terrestrial biogeochemistry models forced with MPWP climate model simulations from four different climate models to produce a comprehensive reconstruction of the MPWP CH4cycle, including uncertainty. We simulate an atmospheric CH4mixing ratio of 1,000 to 1,200 ppbv, which in combination with estimates of radiative forcing from N2O and O3, contributes a non-CO2radiative forcing of 0.9W⋅m−2(range 0.6 to 1.1), which is 43% (range 36 to 56%) of the CO2radiative forcing used in MPWP climate simulations. This additional forcing would cause a global surface temperature increase of 0.6 to 1.0 °C, with amplified changes at high latitudes, improving agreement with geological evidence of Middle Pliocene climate. We conclude that natural trace gas feedbacks are critical for interpreting climate warmth during the Pliocene and potentially many other warm phases of the Cenezoic. These results also imply that using Pliocene CO2and temperature reconstructions alone may lead to overestimates of the fast or Charney climate sensitivity.

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