Responses of Tropical and Subtropical High-Cloud Statistics to Global Warming

Abstract Data from global high-resolution, nonhydrostatic simulations, covering a 1-yr period and with horizontal grid sizes of 7 and 14 km, were analyzed to evaluate the response of high cloud to global warming. The results indicate that, in a warmer atmosphere, high-cloud cover increases robustly and associated longwave (LW) cloud radiative forcing (CRF) increases on average. To develop a better understanding of high-cloud responses to climate change, the geographical distribution of high-cloud size obtained from the model was analyzed and compared with observations. In warmer atmospheres, the contribution per cloud to CRF decreases for both the LW and shortwave (SW) components. However, because of significant increases in the numbers of high clouds in almost all cloud size categories, the magnitude of both LW and SW CRF increases in the simulations. In particular, the contribution from an increase in the number of smaller clouds has more effect on the CRF change. It was also found that the ice and liquid water paths decrease in smaller clouds and that particularly the former contributes to reduced LW CRF per high cloud.

Download Full-text

A Climatology of Midlatitude Continental Clouds from the ARM SGP Central Facility. Part II: Cloud Fraction and Surface Radiative Forcing

Journal of Climate ◽

10.1175/jcli3710.1 ◽

2006 ◽

Vol 19 (9) ◽

pp. 1765-1783 ◽

Cited By ~ 81

Author(s):

Xiquan Dong ◽

Baike Xi ◽

Patrick Minnis

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

Cloud Cover ◽

Surface Albedo ◽

Cloud Fraction ◽

Total Cloud Cover ◽

Cloud Radiative Forcing ◽

Low Clouds ◽

High Clouds ◽

Central Facility

Abstract Data collected at the Department of Energy Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Central Facility (SCF) are analyzed to determine the monthly and hourly variations of cloud fraction and radiative forcing between January 1997 and December 2002. Cloud fractions are estimated for total cloud cover and for single-layered low (0–3 km), middle (3–6 km), and high clouds (>6 km) using ARM SCF ground-based paired lidar–radar measurements. Shortwave (SW) and longwave (LW) fluxes are derived from up- and down-looking standard precision spectral pyranometers and precision infrared radiometer measurements with uncertainties of ∼10 W m−2. The annual averages of total and single-layered low-, middle-, and high-cloud fractions are 0.49, 0.11, 0.03, and 0.17, respectively. Both total- and low-cloud amounts peak during January and February and reach a minimum during July and August; high clouds occur more frequently than other types of clouds with a peak in summer. The average annual downwelling surface SW fluxes for total and low clouds (151 and 138 W m−2, respectively) are less than those under middle and high clouds (188 and 201 W m−2, respectively), but the downwelling LW fluxes (349 and 356 W m−2) underneath total and low clouds are greater than those from middle and high clouds (337 and 333 W m−2). Low clouds produce the largest LW warming (55 W m−2) and SW cooling (−91 W m−2) effects with maximum and minimum absolute values in spring and summer, respectively. High clouds have the smallest LW warming (17 W m−2) and SW cooling (−37 W m−2) effects at the surface. All-sky SW cloud radiative forcing (CRF) decreases and LW CRF increases with increasing cloud fraction with mean slopes of −0.984 and 0.616 W m−2 %−1, respectively. Over the entire diurnal cycle, clouds deplete the amount of surface insolation more than they add to the downwelling LW flux. The calculated CRFs do not appear to be significantly affected by uncertainties in data sampling and clear-sky screening. Traditionally, cloud radiative forcing includes not only the radiative impact of the hydrometeors, but also the changes in the environment. Taken together over the ARM SCF, changes in humidity and surface albedo between clear and cloudy conditions offset ∼20% of the NET radiative forcing caused by the cloud hydrometeors alone. Variations in water vapor, on average, account for 10% and 83% of the SW and LW CRFs, respectively, in total cloud cover conditions. The error analysis further reveals that the cloud hydrometeors dominate the SW CRF, while water vapor changes are most important for LW flux changes in cloudy skies. Similar studies over other locales are encouraged where water and surface albedo changes from clear to cloudy conditions may be much different than observed over the ARM SCF.

Download Full-text

Robust increase of Indian monsoon rainfall and its variability under future warming in CMIP-6 models

10.5194/esd-2020-80 ◽

2020 ◽

Author(s):

Anja Katzenberger ◽

Jacob Schewe ◽

Julia Pongratz ◽

Anders Levermann

Keyword(s):

Climate Change ◽

Global Warming ◽

Climate Models ◽

Monsoon Rainfall ◽

Global Climate ◽

Coupled Model ◽

Global Climate Models ◽

Future Climate Change ◽

Global Mean Temperature ◽

Almost All

Abstract. The Indian summer monsoon is an integral part of the global climate system. As its seasonal rainfall plays a crucial role in India's agriculture and shapes many other aspects of life, it affects the livelihood of a fifth of the world's population. It is therefore highly relevant to assess its change under potential future climate change. Global climate models within the Coupled Model Intercomparison Project Phase 5 (CMIP-5) indicated a consistent increase in monsoon rainfall and its variability under global warming. Since the range of the results of CMIP-5 was still large and the confidence in the models was limited due to partly poor representation of observed rainfall, the updates within the latest generation of climate models in CMIP-6 are of interest. Here, we analyse 32 models of the latest CMIP-6 exercise with regard to their annual mean monsoon rainfall and its variability. All of these models show a substantial increase in June-to-September (JJAS) mean rainfall under unabated climate change (SSP5-8.5) and most do also for the other three Shared Socioeconomic Pathways analyzed (SSP1-2.6, SSP2-4.5, SSP3-7.0). Moreover, the simulation ensemble indicates a linear dependence of rainfall on global mean temperature with high agreement between the models and independent of the SSP; the multi-model mean for JJAS projects an increase of 0.33 mm/day and 5.3 % per degree of global warming. This is significantly higher than in the CMIP-5 projections. Most models project that the increase will contribute to the precipitation especially in the Himalaya region and to the northeast of the Bay of Bengal, as well as the west coast of India. Interannual variability is found to be increasing in the higher-warming scenarios by almost all models. The CMIP-6 simulations largely confirm the findings from CMIP-5 models, but show an increased robustness across models with reduced uncertainties and updated magnitudes towards a stronger increase in monsoon rainfall.

Download Full-text

Cloud radiative forcing intercomparison between fully coupled CMIP5 models and CERES satellite data

Annales Geophysicae ◽

10.5194/angeo-32-793-2014 ◽

2014 ◽

Vol 32 (7) ◽

pp. 793-807 ◽

Cited By ~ 26

Author(s):

M. Calisto ◽

D. Folini ◽

M. Wild ◽

L. Bengtsson

Keyword(s):

Radiative Forcing ◽

Cloud Cover ◽

Coupled Model ◽

Cmip5 Models ◽

Radiative Fluxes ◽

Cloud Radiative Forcing ◽

Summer Hemisphere ◽

Intercomparison Project ◽

Annual Means ◽

The Tropics

Abstract. In this paper, radiative fluxes for 10 years from 11 models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) and from CERES satellite observations have been analyzed and compared. Under present-day conditions, the majority of the investigated CMIP5 models show a tendency towards a too-negative global mean net cloud radiative forcing (NetCRF) as compared to CERES. A separate inspection of the long-wave and shortwave contribution (LWCRF and SWCRF) as well as cloud cover points to different shortcomings in different models. Models with a similar NetCRF still differ in their SWCRF and LWCRF and/or cloud cover. Zonal means mostly show excessive SWCRF (too much cooling) in the tropics between 20° S and 20° N and in the midlatitudes between 40 to 60° S. Most of the models show a too-small/too-weak LWCRF (too little warming) in the subtropics (20 to 40° S and N). Difference maps between CERES and the models identify the tropical Pacific Ocean as an area of major discrepancies in both SWCRF and LWCRF. The summer hemisphere is found to pose a bigger challenge for the SWCRF than the winter hemisphere. The results suggest error compensation to occur between LWCRF and SWCRF, but also when taking zonal and/or annual means. Uncertainties in the cloud radiative forcing are thus still present in current models used in CMIP5.

Download Full-text

Not all biodiversity rich spots are climate refugia

Biogeosciences ◽

10.5194/bg-18-6567-2021 ◽

2021 ◽

Vol 18 (24) ◽

pp. 6567-6578

Author(s):

Ádám T. Kocsis ◽

Qianshuo Zhao ◽

Mark J. Costello ◽

Wolfgang Kiessling

Keyword(s):

Climate Change ◽

Global Warming ◽

Global Scale ◽

Absolute Temperature ◽

Elevated Risk ◽

Anthropogenic Climate Change ◽

Range Shifts ◽

Future Warming ◽

Almost All

Abstract. Anthropogenic climate change is increasingly threatening biodiversity on a global scale. Rich spots of biodiversity, regions with exceptionally high endemism and/or number of species, are a top priority for nature conservation. Terrestrial studies have hypothesized that rich spots occur in places where long-term climate change was dampened relative to other regions. Here we tested whether biodiversity rich spots are likely to provide refugia for organisms during anthropogenic climate change. We assessed the spatial distribution of both historic (absolute temperature change and climate change velocities) and projected climate change in terrestrial, freshwater, and marine rich spots. Our analyses confirm the general consensus that global warming will impact almost all rich spots of all three realms and suggest that their characteristic biota is expected to witness similar forcing to other areas, including range shifts and elevated risk of extinction. Marine rich spots seem to be particularly sensitive to global warming: they have warmed more, have higher climate velocities, and are projected to experience higher future warming than non-rich-spot areas. However, our results also suggest that terrestrial and freshwater rich spots will be somewhat less affected than other areas. These findings emphasize the urgency of protecting a comprehensive and representative network of biodiversity-rich areas that accommodate species range shifts under climate change.

Download Full-text

Aerosol-driven droplet concentrations dominate coverage and water of oceanic low-level clouds

Science ◽

10.1126/science.aav0566 ◽

2019 ◽

Vol 363 (6427) ◽

pp. eaav0566 ◽

Cited By ~ 63

Author(s):

Daniel Rosenfeld ◽

Yannian Zhu ◽

Minghuai Wang ◽

Youtong Zheng ◽

Tom Goren ◽

...

Keyword(s):

Radiative Forcing ◽

Cloud Cover ◽

Climate Models ◽

Cloud Condensation Nuclei ◽

Climate Forcing ◽

Present Climate ◽

Cloud Radiative Forcing ◽

Cloud Properties ◽

Aerosol Effects ◽

Meteorological Effects

A lack of reliable estimates of cloud condensation nuclei (CCN) aerosols over oceans has severely limited our ability to quantify their effects on cloud properties and extent of cooling by reflecting solar radiation—a key uncertainty in anthropogenic climate forcing. We introduce a methodology for ascribing cloud properties to CCN and isolating the aerosol effects from meteorological effects. Its application showed that for a given meteorology, CCN explains three-fourths of the variability in the radiative cooling effect of clouds, mainly through affecting shallow cloud cover and water path. This reveals a much greater sensitivity of cloud radiative forcing to CCN than previously reported, which means too much cooling if incorporated into present climate models. This suggests the existence of compensating aerosol warming effects yet to be discovered, possibly through deep clouds.

Download Full-text

Diurnal Cycles of Clouds and How They Affect Polar-Orbiting Satellite Data

Journal of Climate ◽

10.1175/2007jcli2027.1 ◽

2008 ◽

Vol 21 (16) ◽

pp. 3989-3996 ◽

Cited By ~ 13

Author(s):

Donald Wylie

Keyword(s):

High Resolution ◽

Satellite Data ◽

Cloud Cover ◽

Time Trend ◽

Summer Season ◽

High Cloud ◽

Diurnal Cycles ◽

The Earth ◽

Polar Orbiting Satellite ◽

Infrared Data

Abstract Diurnal cycles of clouds were investigated using the NOAA series of polar-orbiting satellites. These satellites provided four observations per day for a continuous 11-yr period from 1986 to 1997. The High Resolution Infrared Radiation Sounder (HIRS) multispectral infrared data were used from the time trend analysis of Wylie et al. The previous study restricted its discussion to only the polar orbiters making observations at 0200 and 1400 LT because gaps in coverage occurred in the 0800 and 2000 LT coverage. This study shows diurnal cycles in cloud cover over 10% in amplitude in many regions, which is very similar to other studies that used geostationary satellite data. The use of only one of the polar-orbiting satellites by Wylie et al. caused biases up to 5% in small regions but in general they were small (e.g., ≤2% for most of the earth). The only consistently large bias was in high cloud cover over land in North America, Europe, and Asia north of 35°N latitude in the summer season where the 0200 and 1400 LT average high cloud frequency was 2%–5% more than the daily average. This occurred only in the summer season, not in the winter.

Download Full-text

Municipal Young Assembly

Open Schools Journal for Open Science ◽

10.12681/osj.23425 ◽

2020 ◽

Vol 3 ◽

Author(s):

H. Paixão ◽

S. Romeiro

Keyword(s):

Climate Change ◽

Global Warming ◽

Young People ◽

Final Session ◽

8Th Grade ◽

Almost All ◽

Academic Year

This project results from the need to encourage young people to actively participate in the life of the Municipality. In the 2018/2019 academic year, the theme “Climate change: reversing global warming” was worked on in almost all curricular areas, in two 8th grade classes of the school. The classes elected their own "Young Municipal Deputies". Throughout the project, students were prepared for the final session, where each school represented a party and allparties presented and defended their proposals, to all the Assembly.

Download Full-text

Switching cloud cover and dynamical regimes from open to closed Benard cells in response to the suppression of precipitation by aerosols

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-6-1179-2006 ◽

2006 ◽

Vol 6 (1) ◽

pp. 1179-1198 ◽

Cited By ~ 2

Author(s):

D. Rosenfeld ◽

Y. J. Kaufman ◽

I. Koren

Keyword(s):

Boundary Layer ◽

Radiative Forcing ◽

Cloud Cover ◽

Marine Boundary Layer ◽

Background Level ◽

Dynamic Structure ◽

Positive Feedbacks ◽

Cloud Radiative Forcing ◽

Cloud Regime ◽

Dynamical Regimes

Abstract. The dynamic structure of the atmospheric marine boundary layer (MBL) supports two distinct states of cloud cover: closed and open Benard cellular convection. Closed cells are nearly fully cloud covered, while the open cells have <40% cloud cover. Here we show that aerosols have a greater than expected impact on the cloud cover by changing the mode of cellular convection. By suppressing precipitation aerosols can reverse the direction of the airflow, converting the cloud structure from open to closed cells and doubling the cloud cover. The two states possess positive feedbacks for self maintenance, so that small changes of the conditions can lead to bifurcation of the MBL cloud regime. The transition occurs at near pristine background level of aerosols, creating a large sensitivity of cloud radiative forcing to very small changes in aerosols at the MBL. This can have a major impact on global temperatures.

Download Full-text

Discovery of the Major Mechanism of Global Warming and Climate Change

10.31219/osf.io/9r6gf ◽

2018 ◽

Author(s):

Paul C. Rivera

Keyword(s):

Climate Change ◽

Global Warming ◽

Greenhouse Gases ◽

Solar Irradiance ◽

Radiative Forcing ◽

Climate Model ◽

Radiative Flux ◽

North Pole ◽

Major Mechanism ◽

Solar Radiative Flux

Statistical analysis of the number of destructive earthquakes versus global temperature and greenhouse gases revealed very significant correlations. The motion of the North Pole, deduced from the geomagnetic polar shift data, is highly correlated with major earthquakes. This is an indication that the frequent occurrence of major earthquakes had increased earth’s obliquity and possibly induced global warming and emission of greenhouse gases. It was shown by a simple model developed here that seismic-induced oceanic force could enhance the obliquity leading to increased solar radiative flux on earth. The increase of the absorbed solar radiation due to polar tilt was also confirmed by SOLRAD model which computed a net gain of solar radiative forcing due to enhanced obliquity. SOLRAD also revealed a poleward gain of solar radiative flux which could have facilitated the observed polar amplification of global warming. Multiple regression analysis also showed that polar shift and solar irradiance played a major role in the temperature rise and CO2 increase in recent years. The analysis showed that obliquity change due to North Pole shift and total solar irradiance accounted for 63.5% and 36.4% respectively, while CO2 changes accounted for 0.1% of the observed global warming. Preliminary simulations conducted with EdGCM climate model also showed that enhanced obliquity increases the absorbed solar radiative flux, surface air and ocean temperatures, and decreases ocean ice cover. This study confirmed in several ways that earthquake-perturbed obliquity change, and not greenhouse effect, is the major mechanism governing the present global warming and climate change problem.

Download Full-text

Spectral and Broadband Longwave Downwelling Radiative Fluxes, Cloud Radiative Forcing, and Fractional Cloud Cover over the South Pole

Journal of Climate ◽

10.1175/jcli3525.1 ◽

2005 ◽

Vol 18 (20) ◽

pp. 4235-4252 ◽

Cited By ~ 32

Author(s):

Michael S. Town ◽

Von P. Walden ◽

Stephen G. Warren

Keyword(s):

Water Vapor ◽

Radiative Forcing ◽

Cloud Cover ◽

South Pole ◽

The South ◽

Near Surface ◽

Cloud Radiative Forcing ◽

Clear Sky ◽

Fractional Cloud ◽

Visual Observations

Abstract Annual cycles of downwelling broadband infrared radiative flux and spectral downwelling infrared flux were determined using data collected at the South Pole during 2001. Clear-sky conditions are identified by comparing radiance ratios of observed and simulated spectra. Clear-sky fluxes are in the range of 110–125 W m−2 during summer (December–January) and 60–80 W m−2 during winter (April–September). The variability is due to day-to-day variations in temperature, strength of the surface-based temperature inversion, atmospheric humidity, and the presence of “diamond dust” (near-surface ice crystals). The persistent presence of diamond dust under clear skies during the winter is evident in monthly averages of clear-sky radiance. About two-thirds of the clear-sky flux is due to water vapor, and one-third is due to CO2, both in summer and winter. The seasonal constancy of this approximately 2:1 ratio is investigated through radiative transfer modeling. Precipitable water vapor (PWV) amounts were calculated to investigate the H2O/CO2 flux ratio. Monthly mean PWV during 2001 varied from 1.6 mm during summer to 0.4 mm during winter. Earlier published estimates of PWV at the South Pole are similar for winter, but are 50% lower for summer. Possible reasons for low earlier estimates of summertime PWV are that they are based either on inaccurate hygristor technology or on an invalid assumption that the humidity was limited by saturation with respect to ice. The average fractional cloud cover derived from the spectral infrared data is consistent with visual observations in summer. However, the wintertime average is 0.3–0.5 greater than that obtained from visual observations. The annual mean of longwave downwelling cloud radiative forcing (LDCRF) for 2001 is about 23 W m−2 with no apparent seasonal cycle. This is about half that of the global mean LDCRF; the low value is attributed to the small optical depths and low temperatures of Antarctic clouds.

Download Full-text