The Canadian Centre for Climate Modelling and Analysis (CCCma) has developed the fourth generation of the Canadian Atmospheric Global Climate Model (CanAM4). The new model includes substantially modified physical parameterizations compared to its predecessor. In particular, the treatment of clouds, cloud radiative effects, and precipitation has been modified. Aerosol direct and indirect effects are calculated based on a bulk aerosol scheme. Simulation results for present-day global climate are analyzed, with a focus on cloud radiative effects and precipitation. Good overall agreement is found between climatological mean short- and longwave cloud radiative effects and observations from the Clouds and Earth's Radiant Energy System (CERES) experiment. An analysis of the responses of cloud radiative effects to variations in climate will be presented in a companion paper. [Traduit par la redaction] Le Centre canadien de la modelisation et de l'analyse climatique (CCmaC) a mis au point la quatrieme generation d...

https://www.tandfonline.com/doi/pdf/10.1080/07055900.2012.755610

The Canadian Fourth Generation Atmospheric Global Climate Model (CanAM4). Part I: Representation of Physical Processes

For the current generation of earth system models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), the range of equilibrium climate sensitivity (ECS, a hypothetical value of global warming at equilibrium for a doubling of CO2) is 18°C to 56°C, the largest of any generation of models dating to the 1990s Meanwhile, the range of transient climate response (TCR, the surface temperature warming around the time of CO2 doubling in a 1% per year CO2 increase simulation) for the CMIP6 models of 17°C (13°C to 30°C) is only slightly larger than for the CMIP3 and CMIP5 models Here we review and synthesize the latest developments in ECS and TCR values in CMIP, compile possible reasons for the current values as supplied by the modeling groups, and highlight future directions Cloud feedbacks and cloud-aerosol interactions are the most likely contributors to the high values and increased range of ECS in CMIP6

Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models.

Abstract In recent decades, the warming in the Arctic has been much faster than in the rest of the world, a phenomenon known as Arctic amplification. Numerous studies report that the Arctic is warming either twice, more than twice, or even three times as fast as the globe on average. Here we show, by using several observational datasets which cover the Arctic region, that during the last 43 years the Arctic has been warming nearly four times faster than the globe, which is a higher ratio than generally reported in literature. We compared the observed Arctic amplification ratio with the ratio simulated by state-of-the-art climate models, and found that the observed four-fold warming ratio over 1979–2021 is an extremely rare occasion in the climate model simulations. The observed and simulated amplification ratios are more consistent with each other if calculated over a longer period; however the comparison is obscured by observational uncertainties before 1979. Our results indicate that the recent four-fold Arctic warming ratio is either an extremely unlikely event, or the climate models systematically tend to underestimate the amplification. 

/pdf/the-arctic-has-warmed-nearly-four-times-faster-than-the-2f7lp97b.pdf

The Arctic has warmed nearly four times faster than the globe since 1979

. Anthropogenic climate change is projected to lead to ocean warming, acidification, deoxygenation,
reductions in near-surface nutrients, and changes to primary production, all of which are expected
to affect marine ecosystems. Here we assess projections of these drivers of environmental change
over the twenty-first century from Earth system models (ESMs) participating in the Coupled Model
Intercomparison Project Phase 6 (CMIP6) that were forced under the CMIP6 Shared Socioeconomic
Pathways (SSPs). Projections are compared to those from the previous generation (CMIP5) forced
under the Representative Concentration Pathways (RCPs). A total of 10 CMIP5 and 13 CMIP6 models are used in
the two multi-model ensembles. Under the high-emission scenario SSP5-8.5, the multi-model global
mean change (2080–2099 mean values relative to 1870–1899) ± the inter-model SD in sea
surface temperature, surface pH, subsurface (100–600  m ) oxygen concentration, euphotic
(0–100  m ) nitrate concentration, and depth-integrated primary production is
 + 3.47 ± 0.78 ∘C , - 0.44 ± 0.005 , - 13.27 ± 5.28 ,
 - 1.06 ± 0.45 mmol m−3 and - 2.99 ± 9.11  %, respectively. Under the
low-emission, high-mitigation scenario SSP1-2.6, the corresponding global changes are
 + 1.42 ± 0.32 ∘C , - 0.16 ± 0.002 , - 6.36 ± 2.92 ,
 - 0.52 ± 0.23 mmol m−3 , and - 0.56 ± 4.12  %. Projected exposure of the marine
ecosystem to these drivers of ocean change depends largely on the extent of future emissions,
consistent with previous studies. The ESMs in CMIP6 generally project greater warming,
acidification, deoxygenation, and nitrate reductions but lesser primary production declines than
those from CMIP5 under comparable radiative forcing. The increased projected ocean warming results
from a general increase in the climate sensitivity of CMIP6 models relative to those of
CMIP5. This enhanced warming increases upper-ocean stratification in CMIP6 projections, which
contributes to greater reductions in upper-ocean nitrate and subsurface oxygen ventilation. The
greater surface acidification in CMIP6 is primarily a consequence of the SSPs having higher
associated atmospheric CO2 concentrations than their RCP analogues for the same
radiative forcing. We find no consistent reduction in inter-model uncertainties, and even an
increase in net primary
production inter-model uncertainties in CMIP6, as compared to CMIP5.

/pdf/twenty-first-century-ocean-warming-acidification-2b9m6j9g04.pdf

Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projections

The latest Coupled Model Intercomparison Project phase 6 (CMIP6) dataset was analyzed to examine the projected changes in temperature and precipitation over six South Asian countries during the twenty-first century. The CMIP6 model simulations reveal biases in annual mean temperature and precipitation over South Asia in the present climate. In the historical period, the median of the CMIP6 model ensemble systematically underestimates the annual mean temperature for all the South Asian countries, while a mixed behavior is shown in the case of precipitation. In the future climate, the CMIP6 models display higher sensitivity to greenhouse gas emissions over South Asia compared with the CMIP5 models. The multimodel ensemble from 27 CMIP6 models projects a continuous increase in the annual mean temperature over South Asia during the twenty-first century under three future scenarios. The projected temperature shows a large increase (over 6 °C under SSP5-8.5 scenario) over the northwestern parts of South Asia, comprising the complex Karakorum and Himalayan mountain ranges. Any large increase in the mean temperature over this region will most likely result in a faster rate of glacier melting. By the end of the twenty-first century, the annual mean temperature (uncertainty range) over South Asia is projected to increase by 1.2 (0.7–2.1) °C, 2.1 (1.5–3.3) °C, and 4.3 (3.2–6.6) °C under the SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios, respectively, relative to the present (1995–2014) climate. The warming over South Asia is also continuous on the seasonal time scale. The CMIP6 models projected higher warming in the winter season than in the summer over South Asia, which if verified will have repercussions for snow/ice accumulations as well as winter cropping patterns. The annual mean precipitation is also projected to increase over South Asia during the twenty-first century under all scenarios. The rate of change in the projected annual mean precipitation varies considerably between the South Asian countries. By the end of the twenty-first century, the country-averaged annual mean precipitation (uncertainty range) is projected to increase by 17.1 (2.2–49.1)% in Bangladesh, 18.9 (−4.9 to 72)% in Bhutan, 27.3 (5.3–160.5)% in India, 19.5 (−5.9 to 95.6)% in Nepal, 26.4 (6.4–159.7)% in Pakistan, and 25.1 (−8.5 to 61.0)% in Sri Lanka under the SSP5-8.5 scenario. The seasonal precipitation projections also shows large variability. The projected winter precipitation reveals a robust increase over the western Himalayas, with a corresponding decrease over the eastern Himalayas. On the other hand, the summer precipitation shows a robust increase over most of the South Asia region, with the largest increase over the arid region of southern Pakistan and adjacent areas of India, under the high-emission scenario. The results presented in this study give detailed insights into CMIP6 model performance over the South Asia region, which could be extended further to develop adaptation strategies, and may act as a guideline document for climate change related policymaking in the region.

/pdf/projections-of-precipitation-and-temperature-over-the-south-27t03b9ls3.pdf

Projections of Precipitation and Temperature over the South Asian Countries in CMIP6

. The Canadian Earth System Model version 5 (CanESM5) is a global
model developed to simulate historical climate change and variability, to
make centennial-scale projections of future climate, and to produce
initialized seasonal and decadal predictions. This paper describes the model
components and their coupling, as well as various aspects of model
development, including tuning, optimization, and a reproducibility strategy.
We also document the stability of the model using a long control simulation,
quantify the model's ability to reproduce large-scale features of the
historical climate, and evaluate the response of the model to external
forcing. CanESM5 is comprised of three-dimensional atmosphere (T63 spectral
resolution equivalent roughly to 2.8 ∘ ) and ocean (nominally 1 ∘ ) general
circulation models, a sea-ice model, a land surface scheme, and explicit
land and ocean carbon cycle models. The model features relatively coarse
resolution and high throughput, which facilitates the production of large
ensembles. CanESM5 has a notably higher equilibrium climate sensitivity
(5.6 K) than its predecessor, CanESM2 (3.7 K), which we briefly discuss, along
with simulated changes over the historical period. CanESM5 simulations
contribute to the Coupled Model Intercomparison Project phase 6 (CMIP6)
and will be employed for climate science and service applications in Canada.

/pdf/the-canadian-earth-system-model-version-5-canesm5-0-3-3yhcmcmmeu.pdf

The Canadian Earth System Model version 5 (CanESM5.0.3)

An analysis of several ocean surface albedo (OSA) schemes is undertaken through offline comparisons and through application in the Canadian Centre for Climate Modelling and Analysis (CCCma) fourthgeneration atmospheric general circulation model (AGCM4). In general, each scheme requires different input quantities to determine the OSA. Common to all schemes is a dependence on the solar zenith angle (SZA). A direct comparison of the SZA dependence of the schemes reveals significant differences in the predicted albedos. Other input quantities include wind speed and aerosol/cloud optical depth, which are also analyzed. An offline one-dimensional radiative transfer model is used to quantitatively study the impact of ocean surface albedo on the radiative transfer process. It is found that, as a function of SZA and wind speed, the difference in reflected solar flux at the top of the atmosphere is in general agreement between OSA schemes that depend on these quantities, with a difference 10 Wm 2 . However, for simpler schemes that depend only on SZA the difference in this flux can approach 10–20 W m 2 . The impact of the different OSA schemes is assessed through multiyear simulations of present-day climate in AGCM4. Five-year means of the reflected clear-sky flux at the top of the atmosphere reveal local differences of up to several watts per meters squared between any of the schemes. Globally, all schemes display a similar negative bias relative to the Earth Radiation Budget Experiment (ERBE) observations. This negative bias is largely reduced by comparison with the recently released Clouds and the Earth’s Radiant Energy System (CERES) data. It is shown that the local upward clear-sky flux at the surface is more sensitive to the OSA formulation than the clear-sky upward flux at the top of atmosphere. It is found that the global energy balance of the model at the top of the atmosphere and at the surface is surprisingly insensitive to which OSA scheme is employed.

Mike Lazare

Papers

The Canadian Earth System Model version 5 (CanESM5.0.3)

Ocean Surface Albedo and Its Impact on Radiation Balance in Climate Models

CMIP6.ScenarioMIP.CCCma.CanESM5

CMIP6.ScenarioMIP.CCCma.CanESM5.ssp585

CMIP6.ScenarioMIP.CCCma.CanESM5.ssp245