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Effective radiative forcing and adjustments in CMIP6 models
The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W/sq. m, comprised of 1.81 (±0.09) W/sq. m from CO2, 1.08 (± 0.21) W/sq. m from other well-mixed greenhouse gases, −1.01 (± 0.23) W/sq. m from aerosols and −0.09 (±0.13) W/sq. m from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W/sq. m. The majority of the remaining 0.21 W/sq. m is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W/sq. m, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.
Journal Article
The amazing unity of the universe : and its origin in the big bang
In the first chapters the author describes how our knowledge of the position of Earth in space and time has developed, thanks to the work of many generations of astronomers and physicists. He discusses how our position in the Galaxy was discovered, and how in 1929, Hubble uncovered the fact that the Universe is expanding, leading to the picture of the Big Bang. He then explains how astronomers have found that the laws of physics that were discovered here on Earth and in the Solar System (the laws of mechanics, gravity, atomic physics, electromagnetism, etc.) are valid throughout the Universe. This is illustrated by the fact that all matter in the Universe consists of atoms of the same chemical elements that we know on Earth. This unity is all the more surprising when one realizes that in the original Big Bang theory, different parts of the Universe could never have communicated with each other.
Book
Near-real-time monitoring of global CO2 emissions reveals the effects of the COVID-19 pandemic
The COVID-19 pandemic is impacting human activities, and in turn energy use and carbon dioxide (CO
2
) emissions. Here we present daily estimates of country-level CO
2
emissions for different sectors based on near-real-time activity data. The key result is an abrupt 8.8% decrease in global CO
2
emissions (−1551 Mt CO
2
) in the first half of 2020 compared to the same period in 2019. The magnitude of this decrease is larger than during previous economic downturns or World War II. The timing of emissions decreases corresponds to lockdown measures in each country. By July 1st, the pandemic’s effects on global emissions diminished as lockdown restrictions relaxed and some economic activities restarted, especially in China and several European countries, but substantial differences persist between countries, with continuing emission declines in the U.S. where coronavirus cases are still increasing substantially.
The COVID-19 pandemic has stopped many human activities, which has had significant impact on emissions of greenhouse gases. Here, the authors present daily estimates of country-level CO
2
emissions for different economic sectors and show that there has been a 8.8% decrease in global CO2 emissions in the first half of 2020.
Journal Article
Atmospheric dryness reduces photosynthesis along a large range of soil water deficits
Both low soil water content (SWC) and high atmospheric dryness (vapor pressure deficit, VPD) can negatively affect terrestrial gross primary production (GPP). The sensitivity of GPP to soil versus atmospheric dryness is difficult to disentangle, however, because of their covariation. Using global eddy-covariance observations, here we show that a decrease in SWC is not universally associated with GPP reduction. GPP increases in response to decreasing SWC when SWC is high and decreases only when SWC is below a threshold. By contrast, the sensitivity of GPP to an increase of VPD is always negative across the full SWC range. We further find canopy conductance decreases with increasing VPD (irrespective of SWC), and with decreasing SWC on drier soils. Maximum photosynthetic assimilation rate has negative sensitivity to VPD, and a positive sensitivity to decreasing SWC when SWC is high. Earth System Models underestimate the negative effect of VPD and the positive effect of SWC on GPP such that they should underestimate the GPP reduction due to increasing VPD in future climates.
Using global flux tower observations, the authors show that atmospheric dryness always reduces photosynthesis, whereas soil dryness can increase photosynthesis if soil water stores are sufficient.
Journal Article
How big is the universe?
\"Questions about the universe are as popular as they are daunting to answer. Let this book help satiate young readers curiosity about outer space and the universe by answering this important question! Each page is written with accessible, age-appropriate language and paired with visual aids--including tons of photography from NASA--that bring the text to life. Fact boxes with \"Out of this World!\" tidbits add interest throughout the work, while graphic organizers enhance engagement and comprehension. This book will be right at home in any library!\"-- Provided by publisher.
Book
The Similarity between Descartes's and Aristotle's Notion of Space as Place and Res Extensa
No explanation exists in this work for any causal relation between the faculty of nous and what really exists out there.1 This suggests that Aristotle's idea of place as the bulk carrier of a body is not assigned to the universe:2 no place is outside heaven, hence, body neither exists nor can come to exist outside heaven.3 It is true that everybody exists in place-body cannot be infinite.4 However, he adds, place does not pass out of existence when the things in it are annihilated.5 In this bizarre way, Aristotle assures us that place is not a body. [...]nature is governed by given fixed ratios in the case of place. [...]his claim regarding the limits and completeness of the infinite in virtue of something else refers solely to size as limited by the great and the small; hence the mental \"coincides\" with the physical. The use of the method of induction to attain the perfection of the One is impossible, as principles are definite and complete, Aristotle states firmly.\" [...]no other way for a mathematical concept to exist is possible, unless we attribute place to them: they must be assigned position and contact in order to exist, Aristotle avers.\" Descartes uses the example of wax to show that factors other than extension, such as smell, color, and taste change when wax is heated, so they are not essential characteristics; we recognize wax when heated as the same substance as cold wax only by the use of reason.\"
Journal Article
The universe in your hand : a journey through space, time, and beyond
\"Employs the immediacy of simple, direct language to show us, not explain to us, the theories that underpin everything we know about our universe. To understand what happens to a dying star, we are asked to picture ourselves floating in space in front of it. To get acquainted with the quantum world, we are shrunk to the size of an atom and then taken on a journey. Employing everyday similes and metaphors, addressing the reader directly, and writing stories rather than equations renders these astoundingly complex ideas in an immediate and visceral way\"--Dust jacket flap.
Book
FLUXNET-CH₄ SYNTHESIS ACTIVITY
This paper describes the formation of, and initial results for, a new FLUXNET coordination network for ecosystem-scale methane (CH₄) measurements at 60 sites globally, organized by the Global Carbon Project in partnership with other initiatives and regional flux tower networks. The objectives of the effort are presented along with an overview of the coverage of eddy covariance (EC) CH₄ flux measurements globally, initial results comparing CH₄ fluxes across the sites, and future research directions and needs. Annual estimates of net CH₄ fluxes across sites ranged from −0.2 ± 0.02 g C m−2 yr−1 for an upland forest site to 114.9 ± 13.4 g C m−2 yr−1 for an estuarine freshwater marsh, with fluxes exceeding 40 g C m−2 yr−1 at multiple sites. Average annual soil and air temperatures were found to be the strongest predictor of annual CH₄ flux across wetland sites globally. Water table position was positively correlated with annual CH₄ emissions, although only for wetland sites that were not consistently inundated throughout the year. The ratio of annual CH₄ fluxes to ecosystem respiration increased significantly with mean site temperature. Uncertainties in annual CH₄ estimates due to gap-filling and random errors were on average ±1.6 g C m−2 yr−1 at 95% confidence, with the relative error decreasing exponentially with increasing flux magnitude across sites. Through the analysis and synthesis of a growing EC CH₄ flux database, the controls on ecosystem CH₄ fluxes can be better understood, used to inform and validate Earth system models, and reconcile differences between land surface model- and atmospheric-based estimates of CH₄ emissions.
Journal Article