The new Meteorological Research Institute Earth System Model version 2.0 (MRI-ESM2.0) has been developed based on previous models, MRI-CGCM3 and MRI-ESM1, which participated in the fifth phase of the ...Coupled Model Intercomparison Project (CMIP5). These models underwent numerous improvements meant for highly accurate climate reproducibility. This paper describes model formulation updates and evaluates basic performance of its physical components. The new model has nominal horizontal resolutions of 100 km for atmosphere and ocean components, similar to the previous models. The atmospheric vertical resolution is 80 layers, which is enhanced from the 48 layers of its predecessor. Accumulation of various improvements concerning clouds, such as a new stratocumulus cloud scheme, led to remarkable reduction in errors in shortwave, longwave, and net radiation at the top of the atmosphere. The resulting errors are sufficiently small compared with those in the CMIP5 models. The improved radiation distribution brings the accurate meridional heat transport required for the ocean and contributes to a reduced surface air temperature (SAT) bias. MRI-ESM2.0 displays realistic reproduction of both mean climate and interannual variability. For instance, the stratospheric quasi-biennial oscillation can now be realistically expressed through the enhanced vertical resolution and introduction of non-orographic gravity wave drag parameterization. For the historical experiment, MRI-ESM2.0 reasonably reproduces global SAT change for recent decades; however, cooling in the 1950s through the 1960s and warming afterward are overestimated compared with observations. MRI-ESM2.0 has been improved in many aspects over the previous models, MRI-CGCM3 and MRI-ESM1, and is expected to demonstrate superior performance in many experiments planned for CMIP6.
Sixty-six million years ago, an asteroid approximately 9 km in diameter hit the hydrocarbon- and sulfur-rich sedimentary rocks in what is now Mexico. Recent studies have shown that this impact at the ...Yucatan Peninsula heated the hydrocarbon and sulfur in these rocks, forming stratospheric soot and sulfate aerosols and causing extreme global cooling and drought. These events triggered a mass extinction, including dinosaurs, and led to the subsequent macroevolution of mammals. The amount of hydrocarbon and sulfur in rocks varies widely, depending on location, which suggests that cooling and extinction levels were dependent on impact site. Here we show that the probability of significant global cooling, mass extinction, and the subsequent appearance of mammals was quite low after an asteroid impact on the Earth's surface. This significant event could have occurred if the asteroid hit the hydrocarbon-rich areas occupying approximately 13% of the Earth's surface. The site of asteroid impact, therefore, changed the history of life on Earth.
In the Arctic, observed decadal mean surface air temperatures (SATs) were 0.70°C–0.95°C lower around 1970 than those around 1940. The 35‐multimodel ensemble mean of historical simulations in the ...Coupled Model Intercomparison Project Phase 6 (CMIP6) exhibited Arctic surface cooling trend in 1940–1970, which could be attributed to external forcings. Multimodel ensemble means of CMIP6 Detection and Attribution Model Intercomparison Project historical simulations exhibited Arctic surface cooling of −0.22°C (±0.24°C) in 1970 versus 1940 and showed that anthropogenic aerosol forcings contributed to a cooling of −0.65°C (±0.37°C), which was partially offset by a warming of 0.44°C (±0.22°C) due to well‐mixed greenhouse gases. In addition to the anthropogenic aerosol forcings, multidecadal internal variability with a magnitude of 0.47°C was the component primarily contributing to the observed Arctic cooling. We identified a spatial pattern of pan‐Arctic multidecadal cooling due to the internal variability that resembles the 1940–1970 cooling pattern.
Plain Language Summary
Instrumental records show Arctic surface cooling during the mid‐20th century (1940–1970) followed by ongoing rapid warming since 1970. Long‐term global warming has been extensively researched and has been primarily ascribed to anthropogenic greenhouse gas forcing. However, the factors contributing to the mid‐20th century Arctic surface cooling remain poorly constrained. In this work, multimodel analyses using state‐of‐the‐art climate models suggest that external factors may have contributed to the high‐latitude surface cooling observed in 1940–1970. Further analysis shows that both increased anthropogenic aerosols and multidecadal internal variability provide major contributions to the 1940–1970 Arctic surface cooling. By analyzing surface cooling via unforced long‐term climate simulations, we identified a spatial pattern of pan‐Arctic multidecadal cooling, similar to the observed cooling pattern in the Arctic during 1940–1970.
Key Points
Most Coupled Model Intercomparison Project Phase 6/Detection and Attribution Model Intercomparison Project models represent the observed multidecadal surface cooling trend during the mid‐20th century (1940–1970) in the Arctic
Anthropogenic aerosol forcing and multidecadal internal variability are the major components contributing to the 1940–1970 Arctic cooling
We identify a spatial pattern of pan‐Arctic multidecadal cooling due to internal variability that resembles the 1940–1970 cooling pattern
The mass extinction of life 66 million years ago at the Cretaceous/Paleogene boundary, marked by the extinctions of dinosaurs and shallow marine organisms, is important because it led to the ...macroevolution of mammals and appearance of humans. The current hypothesis for the extinction is that an asteroid impact in present-day Mexico formed condensed aerosols in the stratosphere, which caused the cessation of photosynthesis and global near-freezing conditions. Here, we show that the stratospheric aerosols did not induce darkness that resulted in milder cooling than previously thought. We propose a new hypothesis that latitude-dependent climate changes caused by massive stratospheric soot explain the known mortality and survival on land and in oceans at the Cretaceous/Paleogene boundary. The stratospheric soot was ejected from the oil-rich area by the asteroid impact and was spread globally. The soot aerosols caused sufficiently colder climates at mid-high latitudes and drought with milder cooling at low latitudes on land, in addition to causing limited cessation of photosynthesis in global oceans within a few months to two years after the impact, followed by surface-water cooling in global oceans in a few years. The rapid climate change induced terrestrial extinctions followed by marine extinctions over several years.
Aerosol particles were collected at various altitudes in
the Arctic during the Polar Airborne Measurements and Arctic Regional
Climate Model Simulation Project 2018 (PAMARCMiP 2018) conducted in the
...early spring of 2018. The composition, size, number fraction, and mixing state of
individual aerosol particles were analyzed using transmission electron
microscopy (TEM), and their sources and transport were evaluated by
numerical model simulations. We found that sulfate, sea-salt, mineral-dust,
K-bearing, and carbonaceous particles were the major aerosol constituents.
Many particles were composed of two or more compositions that had coagulated
and were coated with sulfate, organic materials, or both. The number
fraction of mineral-dust and sea-salt particles decreased with increasing
altitude. The K-bearing particles increased within a biomass burning (BB)
plume at altitudes > 3900 m, which originated from Siberia.
Chlorine in sea-salt particles was replaced with sulfate at high altitudes.
These results suggest that the sources, transport, and aging of Arctic
aerosols largely vary depending on the altitude and air-mass history. We also
provide the occurrences of solid-particle inclusions (soot, fly-ash, and
Fe-aggregate particles), some of which are light-absorbing particles. They
were mainly emitted from anthropogenic and biomass burning sources and were
embedded within other relatively large host particles. Our TEM measurements
revealed the detailed mixing state of individual particles at various
altitudes in the Arctic. This information facilitates the accurate
evaluation of the aerosol influences on Arctic haze, radiation balance,
cloud formation, and snow/ice albedo when deposited.
The effective radiative forcing (ERF) of anthropogenic gases and aerosols under present-day conditions relative to preindustrial conditions is estimated using the Meteorological Research Institute ...Earth System Model version 2.0 (MRI-ESM2.0) as part of the Radiative Forcing Model Intercomparison Project (RFMIP) and Aerosol and Chemistry Model Intercomparison Project (AerChemMIP), endorsed by the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The global mean total anthropogenic net ERF estimate at the top of the atmosphere is 1.96 W m
−2
and is composed primarily of positive forcings due to carbon dioxide (1.85 W m
−2
), methane (0.71 W m
−2
), and halocarbons (0.30 W m
−2
) and negative forcing due to the total aerosols (− 1.22 W m
−2
). The total aerosol ERF consists of 23% from aerosol-radiation interactions (− 0.32 W m
−2
), 71% from aerosol-cloud interactions (− 0.98 W m
−2
), and slightly from surface albedo changes caused by aerosols (0.08 W m
−2
). The ERFs due to aerosol-radiation interactions consist of opposing contributions from light-absorbing black carbon (BC) (0.25 W m
−2
) and from light-scattering sulfate (− 0.48 W m
−2
) and organic aerosols (− 0.07 W m
−2
) and are pronounced over emission source regions. The ERFs due to aerosol-cloud interactions (ERFaci) are prominent over the source and downwind regions, caused by increases in the number concentrations of cloud condensation nuclei and cloud droplets in low-level clouds. Concurrently, increases in the number concentration of ice crystals in high-level clouds (temperatures < –38 °C), primarily induced by anthropogenic BC aerosols, particularly over tropical convective regions, cause both substantial negative shortwave and positive longwave ERFaci values in MRI-ESM2.0. These distinct forcings largely cancel each other; however, significant longwave radiative heating of the atmosphere caused by high-level ice clouds suggests the importance of further studies on the interactions of aerosols with ice clouds. Total anthropogenic net ERFs are almost entirely positive over the Arctic due to contributions from the surface albedo reductions caused by BC. In the Arctic, BC provides the second largest contribution to the positive ERFs after carbon dioxide, suggesting a possible important role of BC in Arctic surface warming.
Black carbon (BC) particles in the Arctic contribute to
rapid warming of the Arctic by heating the atmosphere and snow and ice
surfaces. Understanding the source contributions to Arctic BC is ...therefore
important, but they are not well understood, especially those for
atmospheric and snow radiative effects. Here we estimate simultaneously the
source contributions of Arctic BC to near-surface and vertically integrated
atmospheric BC mass concentrations (MBC_SRF and
MBC_COL), BC deposition flux (MBC_DEP), and BC radiative effects at the top of the atmosphere and snow
surface (REBC_TOA and REBC_SNOW)
and show that the source contributions to these five variables are highly
different. In our estimates, Siberia makes the largest contribution to
MBC_SRF, MBC_DEP, and
REBC_SNOW in the Arctic (defined as >70∘ N), accounting for 70 %, 53 %, and 41 %, respectively.
In contrast, Asia's contributions to MBC_COL and
REBC_TOA are largest, accounting for 37 % and 43 %,
respectively. In addition, the contributions of biomass burning sources are
larger (29 %–35 %) to MBC_DEP, REBC_TOA, and REBC_SNOW, which are highest from late spring
to summer, and smaller (5.9 %–17 %) to MBC_SRF and
MBC_COL, whose concentrations are highest from winter to
spring. These differences in source contributions to these five variables
are due to seasonal variations in BC emission, transport, and removal
processes and solar radiation, as well as to differences in radiative effect
efficiency (radiative effect per unit BC mass) among sources. Radiative
effect efficiency varies by a factor of up to 4 among sources (1471–5326 W g−1) depending on lifetimes, mixing states, and heights of BC and
seasonal variations of emissions and solar radiation. As a result, source
contributions to radiative effects and mass concentrations (i.e.,
REBC_TOA and MBC_COL, respectively)
are substantially different. The results of this study demonstrate the
importance of considering differences in the source contributions of Arctic
BC among mass concentrations, deposition, and atmospheric and snow radiative
effects for accurate understanding of Arctic BC and its climate impacts.
Vertical profiles of the mass concentration of black carbon (BC) were
measured at altitudes up to 5 km during the PAMARCMiP (Polar Airborne Measurements and Arctic Regional Climate Model simulation ...Project) aircraft-based field
experiment conducted around the northern Greenland Sea (Fram Strait) during
March and April 2018 from operation base Station Nord (81.6∘ N,
16.7∘ W). Median BC mass concentrations in individual altitude
ranges were 7–18 ng m−3 at standard temperature and pressure at
altitudes below 4.5 km. These concentrations were systematically lower than
previous observations in the Arctic in spring, conducted by ARCTAS-A in 2008
and NETCARE in 2015, and similar to those observed during HIPPO3 in 2010.
Column amounts of BC for altitudes below 5 km in the Arctic (>66.5∘ N; COLBC), observed during the ARCTAS-A and NETCARE
experiments, were higher by factors of 4.2 and 2.7, respectively, than those
of the PAMARCMiP experiment. These differences could not be explained solely
by the different locations of the experiments. The year-to-year variation of
COLBC values generally corresponded to that of biomass burning activities
in northern midlatitudes over western and eastern Eurasia. Furthermore,
numerical model simulations estimated the year-to-year variation of
contributions from anthropogenic sources to be smaller than 30 %–40 %.
These results suggest that the year-to-year variation of biomass burning
activities likely affected BC amounts in the Arctic troposphere in spring,
at least in the years examined in this study. The year-to-year variations in
BC mass concentrations were also observed at the surface at high Arctic
sites Ny-Ålesund and Utqiaġvik (formerly known as Barrow, the location of
Barrow Atmospheric Baseline Observatory), although their magnitudes were slightly
lower than those in COLBC. Numerical model simulations in general successfully reproduced the observed
COLBC values for PAMARCMiP and HIPPO3 (within a factor of 2), whereas they
markedly underestimated the values for ARCTAS-A and NETCARE by factors of
3.7–5.8 and 3.3–5.0, respectively. Because anthropogenic contributions
account for nearly all of the COLBC (82 %–98 %) in PAMARCMiP and HIPPO3,
the good agreement between the observations and calculations for these two
experiments suggests that anthropogenic contributions were generally well
reproduced. However, the significant underestimations of COLBC for
ARCTAS-A and NETCARE suggest that biomass burning contributions were
underestimated. In this study, we also investigated plumes with enhanced BC
mass concentrations, which were affected by biomass burning emissions,
observed at 5 km altitude. Interestingly, the mass-averaged diameter of BC
(core) and the shell-to-core diameter ratio of BC-containing particles in
the plumes were generally not very different from those in other air
samples, which were considered to be mostly aged anthropogenic BC. These
observations provide a useful basis to evaluate numerical model simulations of
the BC radiative effect in the Arctic region in spring.
The development of the climate model MRI-ESM2 (Meteorological Research Institute Earth System Model version 2), which is planned for use in the sixth phase of the Coupled Model Intercomparison ...Project (CMIP6) simulations, involved significant improvements to the representation of clouds from the previous version MRI-CGCM3 (Meteorological Research Institute Coupled Global Climate Model version 3), which was used in the CMIP5 simulations. In particular, the serious lack of reflection of solar radiation over the Southern Ocean in MRI-CGCM3 was drastically improved in MRI-ESM2. The score of the spatial pattern of radiative fluxes at the top of the atmosphere for MRI-ESM2 is better than for any CMIP5 model. In this paper, we set out comprehensively the various modifications related to clouds that contribute to the improved cloud representation and the main impacts on the climate of each modification. The modifications cover various schemes and processes including the cloud scheme, turbulence scheme, cloud microphysics processes, interaction between cloud and convection schemes, resolution issues, cloud radiation processes, interaction with the aerosol model, and numerics. In addition, the new stratocumulus parameterization, which contributes considerably to increased low-cloud cover and reduced radiation bias over the Southern Ocean, and the improved cloud ice fall scheme, which alleviates the time-step dependency of cloud ice content, are described in detail.
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