scholarly journals Better calibration of cloud parameterizations and subgrid effects increases the fidelity of E3SM Atmosphere Model version 1

2021 ◽  
Author(s):  
Po-Lun Ma ◽  
Bryce E. Harrop ◽  
Vincent E. Larson ◽  
Richard Neale ◽  
Andrew Gettelman ◽  
...  
Keyword(s):  
Climate Change ◽  
Surface Temperature ◽  
Cloud Microphysics ◽  
Future Climate ◽  
Future Climate Change ◽  
Physical Mechanisms ◽  
The Past ◽  
Model Version ◽  
Atmosphere Model ◽  
Global Mean

Abstract. Realistic simulation of the Earth’s mean state climate remains a major challenge and yet it is crucial for predicting the climate system in transition. Deficiencies in models’ process representations, propagation of errors from one process to another, and associated compensating errors can often confound the interpretation and improvement of model simulations. These errors and biases can also lead to unrealistic climate projections as well as incorrect attribution of the physical mechanisms governing the past and future climate change. Here we show that a significantly improved global atmospheric simulation can be achieved by focusing on the realism of process assumptions in cloud calibration and subgrid effects using the Energy Exascale Earth System Model (E3SM) Atmosphere Model version 1 (EAMv1). The calibration of clouds and subgrid effects informed by our understanding of physical mechanisms leads to significant improvements in clouds and precipitation climatology, reducing common and longstanding biases across cloud regimes in the model. The improved cloud fidelity in turn reduces biases in other aspects of the system. Furthermore, even though the recalibration does not change the global mean aerosol and total anthropogenic effective radiative forcings (ERFs), the sensitivity of clouds, precipitation, and surface temperature to aerosol perturbations is significantly reduced. This suggests that it is possible to achieve improvements to the historical evolution of surface temperature over EAMv1 and that precise knowledge of global mean ERFs is not enough to constrain historical or future climate change. Cloud feedbacks are also significantly reduced in the recalibrated model, suggesting that there would be a lower climate sensitivity when running as part of the fully coupled E3SM. This study also compares results from incremental changes to cloud microphysics, turbulent mixing, deep convection, and subgrid effects to understand how assumptions in the representation of these processes affect different aspects of the simulated atmosphere as well as its response to forcings. We conclude that the spectral composition and geographical distribution of the ERFs and cloud feedback as well as the fidelity of the simulated base climate state are important for constraining the climate in the past and future.

scholarly journals Global mean surface temperature and climate sensitivity of the early Eocene Climatic Optimum (EECO), Paleocene–Eocene Thermal Maximum (PETM), and latest Paleocene

2020 ◽  
Vol 16 (5) ◽  
pp. 1953-1968 ◽  
Author(s):  
Gordon N. Inglis ◽  
Fran Bragg ◽  
Natalie J. Burls ◽  
Margot J. Cramwinckel ◽  
David Evans ◽  
...  
Keyword(s):  
Climate Change ◽  
Surface Temperature ◽  
Climate Sensitivity ◽  
Future Climate Change ◽  
Early Eocene ◽  
Early Eocene Climatic Optimum ◽  
Thermal Maximum ◽  
Global Mean Surface Temperature ◽  
Climatic Optimum ◽  
Global Mean

Abstract. Accurate estimates of past global mean surface temperature (GMST) help to contextualise future climate change and are required to estimate the sensitivity of the climate system to CO2 forcing through Earth's history. Previous GMST estimates for the latest Paleocene and early Eocene (∼57 to 48 million years ago) span a wide range (∼9 to 23 ∘C higher than pre-industrial) and prevent an accurate assessment of climate sensitivity during this extreme greenhouse climate interval. Using the most recent data compilations, we employ a multi-method experimental framework to calculate GMST during the three DeepMIP target intervals: (1) the latest Paleocene (∼57 Ma), (2) the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma), and (3) the early Eocene Climatic Optimum (EECO; 53.3 to 49.1 Ma). Using six different methodologies, we find that the average GMST estimate (66 % confidence) during the latest Paleocene, PETM, and EECO was 26.3 ∘C (22.3 to 28.3 ∘C), 31.6 ∘C (27.2 to 34.5 ∘C), and 27.0 ∘C (23.2 to 29.7 ∘C), respectively. GMST estimates from the EECO are ∼10 to 16 ∘C warmer than pre-industrial, higher than the estimate given by the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (9 to 14 ∘C higher than pre-industrial). Leveraging the large “signal” associated with these extreme warm climates, we combine estimates of GMST and CO2 from the latest Paleocene, PETM, and EECO to calculate gross estimates of the average climate sensitivity between the early Paleogene and today. We demonstrate that “bulk” equilibrium climate sensitivity (ECS; 66 % confidence) during the latest Paleocene, PETM, and EECO is 4.5 ∘C (2.4 to 6.8 ∘C), 3.6 ∘C (2.3 to 4.7 ∘C), and 3.1 ∘C (1.8 to 4.4 ∘C) per doubling of CO2. These values are generally similar to those assessed by the IPCC (1.5 to 4.5 ∘C per doubling CO2) but appear incompatible with low ECS values (<1.5 per doubling CO2).

Simulation of the mid-Pliocene Warm Period using HadGEM3-GC31-LL: Pliocene climate relative to the pre-industrial era, previous model versions, other climate models and proxy data

2021 ◽  
Author(s):  
Charles Williams ◽  
Daniel Lunt ◽  
Alistair Sellar ◽  
William Roberts ◽  
Robin Smith ◽  
...  
Keyword(s):  
Climate Change ◽  
Climate Models ◽  
Climate Model ◽  
High Sensitivity ◽  
Warm Period ◽  
Future Climate ◽  
Future Climate Change ◽  
Last Interglacial ◽  
Proxy Data ◽  
Global Mean

&lt;p&gt;To better understand the processes contributing to future climate change, palaeoclimate model simulations are an important tool because they allow testing of the models&amp;#8217; ability to simulate very different climates than that of today.&amp;#160; As part of CMIP6/PMIP4, the latest version of the UK&amp;#8217;s physical climate model, HadGEM3-GC31-LL (hereafter, for brevity, HadGEM3), was recently used to simulate the mid-Holocene (~6 ka) and Last Interglacial (~127 ka) simulations and the results were compared to the preindustrial era, previous versions of the same model and proxy data (see Williams et al. 2020, Climate of the Past).&amp;#160; Here, we use the same model to go further back in time, presenting the results from the mid-Pliocene Warm Period (~3.3 to 3 ma, hereafter the &amp;#8220;Pliocene&amp;#8221; for brevity).&amp;#160; This period is of particular interest when it comes to projections of future climate change under various scenarios of CO&lt;sub&gt;2&lt;/sub&gt; emissions, because it is the most recent time in Earth&amp;#8217;s history when CO&lt;sub&gt;2&lt;/sub&gt; levels were roughly equivalent to today.&amp;#160; In response, albeit due to slower mechanisms than today&amp;#8217;s anthropogenic fossil fuel driven-change, during the Pliocene global mean temperatures were 2-3&amp;#176;C higher than today, more so at the poles.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Here, we present results from the HadGEM3 Pliocene simulation.&amp;#160; The model is responding to the Pliocene boundary conditions in a manner consistent with current understanding and existing literature.&amp;#160; When compared to the preindustrial era, global mean temperatures are currently ~5&amp;#176;C higher, with the majority of warming coming from high latitudes due to polar amplification from a lack of sea ice.&amp;#160; Relative to other models within the Pliocene Modelling Intercomparison Project (PlioMIP), this is the 2&lt;sup&gt;nd&lt;/sup&gt; warmest model, with the majority of others only showing up to a 4.5&amp;#176;C increase and many a lot less.&amp;#160; This is consistent with the relatively high sensitivity of HadGEM3, relative to other CMIP6-class models.&amp;#160; When compared to a previous generation of the same UK model, HadCM3, similar patterns of both surface temperature and precipitation changes are shown (relative to preindustrial).&amp;#160; Moreover, when the simulations are compared to proxy data, the results suggest that the HadGEM3 Pliocene simulation is closer to the reconstructions than its predecessor.&lt;/p&gt;

Past and future climate change: response by mixed deciduous–coniferous forest ecosystems in northern Michigan

1992 ◽  
Vol 22 (11) ◽  
pp. 1727-1738 ◽  
Author(s):  
Allen M. Solomon ◽  
Patrick J. Bartlein
Keyword(s):  
Climate Change ◽  
Vegetation Dynamics ◽  
Climate Model ◽  
Coniferous Forest ◽  
Mixed Forest ◽  
Future Climate ◽  
Forest Composition ◽  
Future Climate Change ◽  
The Past ◽  
Gap Models

During the 21st century, global climate change is expected to become a significant force redefining global biospheric boundaries and vegetation dynamics. In the northern hardwood–boreal forest transition forests, it should, at the least, control reproductive success and failure among unmanaged mixed forest stands. One means by which to predict future responses by the mixed forests is to examine the way in which they have responded to climate changes in the past. We used proxy climate data derived from Holocene (past 10 000 years) pollen records in the western Upper Peninsula of Michigan to drive forest gap models, in an effort to define regional prehistoric vegetation dynamics on differing soils. The gap models mimic forest reproduction and growth as a successional process and, hence, are appropriate for defining long-term tree and stand dynamics. The modeled period included a mid-postglacial period that was warmer than today's climate. Model failures, made apparent from the exercise, were corrected and the simulations were repeated until the model behaved credibly. Then, the same gap model was used to simulate potential future vegetation dynamics, driven by projections of a future climate that was controlled by greenhouse gases. This provided us with the same "measure" of vegetation in the past, present, and future, generating a continuously comparable record of change and stability in forest composition and density. The resulting projections of vegetation response to climate change appear to be affected more by the rate than by the magnitude of climate change.

scholarly journals Ancient Ocean Floor Seashells Improve Model of Past Glaciers

Eos ◽  
2016 ◽  
Author(s):  
Emily Underwood
Keyword(s):  
Climate Change ◽  
Ice Sheets ◽  
Future Climate ◽  
Ocean Floor ◽  
Future Climate Change ◽  
The Past ◽  
Improve Model ◽  
Accurate Reconstruction

More accurate reconstruction of ice sheets over the past 150,000 years could help scientists predict future climate change.

Climate Change in Eastern Africa

2021 ◽  
Author(s):  
Rob Marchant
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
East Africa ◽  
Future Climate ◽  
Eastern Africa ◽  
Future Climate Change ◽  
Human Populations ◽  
The Past ◽  
Tropical Conditions ◽  
Convergence Zones

The climatology of East Africa results from the complex interaction between major global convergence zones with more localized regional feedbacks to the climate system; these in turn are moderated by a diverse land surface characterized by coastal to land transitions, high mountains, and large lakes. The main climatic character of East Africa, and how this varies across the region, takes the form of seasonal variations in rainfall that can fall as one, two, or three rainy seasons, the times and duration of which will be determined by the interplay between major convergence zones with more localized regional feedbacks. One of the key characteristics of East Africa are climatic variations with altitude as climates change along an altitudinal gradient that can extend from hot, dry, “tropical” conditions to cool, wet, temperate conditions and on the highest mountains “polar” climates with permanent ice caps. With this complex and variable climate landscape of the present, as scientists move through time to explore past climatic variability, it is apparent there have been a series of relatively rapid and high-magnitude environmental shifts throughout East Africa, particularly characterized by changing hydrological budgets. How climate change has impacted on ecosystems, and how those ecosystems have responded and interacted with human populations, can be unearthed by drawing on evidence from the sedimentary and archaeological record of the past six thousand years. As East African economies, and the livelihoods of millions of people in the region, have been clearly heavily affected by climate variability in the past, so it is expected that future climate variability will impact on ecosystem functioning and the preparedness of communities for future climate change.

scholarly journals Warm climates of the past—a lesson for the future?

2013 ◽  
Vol 371 (2001) ◽  
pp. 20130146 ◽  
Author(s):  
D. J. Lunt ◽  
H. Elderfield ◽  
R. Pancost ◽  
A. Ridgwell ◽  
G. L. Foster ◽  
...  
Keyword(s):  
Climate Change ◽  
Numerical Models ◽  
Future Climate ◽  
Future Climate Change ◽  
Climate Data ◽  
Comprehensive Overview ◽  
Past Climate ◽  
The Past ◽  
The Future ◽  
Warm Climates

This Discussion Meeting Issue of the Philosophical Transactions A had its genesis in a Discussion Meeting of the Royal Society which took place on 10–11 October 2011. The Discussion Meeting, entitled ‘Warm climates of the past: a lesson for the future?’, brought together 16 eminent international speakers from the field of palaeoclimate, and was attended by over 280 scientists and members of the public. Many of the speakers have contributed to the papers compiled in this Discussion Meeting Issue. The papers summarize the talks at the meeting, and present further or related work. This Discussion Meeting Issue asks to what extent information gleaned from the study of past climates can aid our understanding of future climate change. Climate change is currently an issue at the forefront of environmental science, and also has important sociological and political implications. Most future predictions are carried out by complex numerical models; however, these models cannot be rigorously tested for scenarios outside of the modern, without making use of past climate data. Furthermore, past climate data can inform our understanding of how the Earth system operates, and can provide important contextual information related to environmental change. All past time periods can be useful in this context; here, we focus on past climates that were warmer than the modern climate, as these are likely to be the most similar to the future. This introductory paper is not meant as a comprehensive overview of all work in this field. Instead, it gives an introduction to the important issues therein, using the papers in this Discussion Meeting Issue, and other works from all the Discussion Meeting speakers, as exemplars of the various ways in which past climates can inform projections of future climate. Furthermore, we present new work that uses a palaeo constraint to quantitatively inform projections of future equilibrium ice sheet change.

scholarly journals A framework for modelling fish and shellfish responses to future climate change

2009 ◽  
Vol 66 (7) ◽  
pp. 1584-1594 ◽  
Author(s):  
Anne Babcock Hollowed ◽  
Nicholas A. Bond ◽  
Thomas K. Wilderbuer ◽  
William T. Stockhausen ◽  
Z. Teresa A'mar ◽  
...  
Keyword(s):  
Climate Change ◽  
Surface Temperature ◽  
Bering Sea ◽  
Environmental Variables ◽  
Future Climate ◽  
Future Climate Change ◽  
Climate Scenarios ◽  
The Mean ◽  
Fish And Shellfish ◽  
The Bering Sea

AbstractHollowed, A. B., Bond, N. A., Wilderbuer, T. K., Stockhausen, W. T., A'mar, Z. T., Beamish, R. J., Overland, J. E., and Schirripa, M. J. 2009. A framework for modelling fish and shellfish responses to future climate change. – ICES Journal of Marine Science, 66: 1584–1594. A framework is outlined for a unified approach to forecasting the implications of climate change on production of marine fish. The framework involves five steps: (i) identification of mechanisms underlying the reproductive success, growth, and distribution of major fish and shellfish populations, (ii) assessment of the feasibility of downscaling implications of climate scenarios derived from Intergovernmental Panel on Climate Change (IPCC) models for regional ecosystems to select and estimate relevant environmental variables, (iii) evaluation of climate model scenarios and select IPCC models that appear to provide valid representations of forcing for the region of study, (iv) extraction of environmental variables from climate scenarios and incorporation into projection models for fish and shellfish, and (v) evaluation of the mean, variance, and trend in fish and shellfish production under a changing ecosystem. This framework was applied to forecast summer sea surface temperature in the Bering Sea from 2001 to 2050. The mean summer surface temperature was predicted to increase by 2°C by 2050. The forecasting framework was also used to estimate the effects of climate change on production of northern rock sole (Lepidopsetta polyxystra) through projected changes in cross-shelf transport of larvae in the Bering Sea. Results suggest that climate change will lead to a modest increase in the production of strong year classes of northern rock sole.

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