Heating in the ocean has continued in 2024 in response to increased greenhouse gas concentrations in the atmosphere, despite the transition from an El Ni&#
The state of knowledge and outstanding challenges and opportunities in global water cycle observations, research and modeling are briefly reviewed to set the stage for the reasons behind the new thrusts promoted by the World Climate Research Programme (WCRP) as Grand...
The hydrological cycle is described. Because the climate is changing from human activities, and there is a direct effect on the hydrological cycle, water resources will also change. The effects of climate change on precipitation, evaporation, and extremes of floods...
Summary form only given. Following a detailed diagnosis of the vital signs of the planet Earth by the IPCC, it has become evident that the planet is running a "fever" and the prognosis is that it is apt to get much worse. "Warming of the climate system is unequivocal" and it is "very likely" due to human activities. This is the verdict of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), known as AR4. Warming of the climate system is unequivocal as is now clear from an increasing body of evidence showing discernible physically consistent changes. Moreover these changes are now simulated in climate models for the past 100 years to a reasonable degree, adding confidence to future projections. This talk will go over the evidence for climate change, how we are able to say that it is due to humans, and what it means for the future.
The flows of energy and water from ocean to land are examined in the context of the land energy and water budgets, for land as a whole and for continents. Most atmospheric reanalyses have large errors of up to 15 W m−2 in the top-of-atmosphere (TOA) energy imbalance, and none include volcanic eruptions. The flow of energy from ocean to land is more reliable as it relies on analyzed wind, temperature, and moisture fields. It is examined for transports of the total, latent energy (LE), and dry static energy (DSE) to land as a whole and as zonal means. The net convergence of energy onto land is balanced by the loss of energy at TOA, measured by Clouds and the Earth’s Radiant Energy System (CERES), and again there are notable discrepancies. Only the ECMWF Interim Re-Analysis (ERA-I) is stable and plausible. Strong compensation between variations in LE and DSE transports onto land means that their sum is more stable over time, and the net transport of energy onto land is largely that associated with the hydrological cycle (LE). A more detailed examination is given of the energy and water budgets for Eurasia, North and South America, Australia, and Africa, making use of Gravity Recovery and Climate Experiment (GRACE) data for water storage on land and data on river discharge into the ocean. With ERA-I, the new land estimates for both water and energy are closer to achieving balances than in previous studies. As well as the annual means, the mean annual cycles are examined in detail along with uncertainty sampling estimates, but the main test used here is that of closure.
A brief review and evaluation of various analyses of the Southern Hemisphere westerlies is given along with the presentation of some relent results. Several features characterize the westerlies of the Southern Hemisphere as quite different from those in the Northern Hemisphere and, in the past, thew have typically been difficult to reproduce well in general circulation modes. They are the double jet structure in winter, the stronger midlatitude tropospheric winds in summer than in winter, and the ensuing much smaller amplitude of the annual cycle which is associated with a maximum of global atmospheric angular momentum in January. New values for the hemispheric angular momentum integrals are than previously reported. Two estimates of the distribution and strength of the southern westerlies that have been widely used are considered to be seriously biased. Factors contributing to discrepancies among different results am large natural variability, missing data and biases in observing systems, and methods of analysis. Over the sparsely observed Southern Hemisphere, the latter is the main reason why biases exist in analyses based only on mean station data, and the absence of imposed dynamical constraints has led to internally inconsistent fields. Even recent estimates of the southern westerlies from global operational analyses should be used judiciously with proper consideration given to reliability and biases.
The advantages and disadvantages of using global analyses on pressure level surfaces versus model (sigma or hybrid) level surfaces are explored. Model levels consist of a terrain-following coordinate in the lowest levels but may gradually transition to pressure with height. One major issue is that the model surface often does not correspond with the earth’s real surface. Another is that a change in horizontal resolution is not well defined because the vertical coordinate also changes in the process. However, such changes are required as comparison of analyses from one center with another or with model output requires a common vertical coordinate. Also, a reduction from high resolution with 106 waves (T106 resolution) to a moderate resolution with, say, 42 waves (T42), so as to reduce the size of datasets by a factor of about 6, is often desirable. Another issue involves the meaning and use of time averages on model surfaces and their relationship to corresponding time averages on pressure surfaces. The traditional representation on constant pressure surfaces has much to recommend it and is widely used and familiar to the community, but suffers from errors arising from interpolation to the pressure surfaces and the need to properly treat regions of those surfaces that are below ground (in regions of high topography). Spectral truncation and resolution changes are well defined on pressure surfaces. Test results are presented for cases where T106 analyses on model surfaces are (1) transformed to pressure and then truncated, (2) truncated and then transformed to pressure levels, and (3) then compared at comparable resolutions. The differences arise mainly from the ill-posed truncation on model surfaces, but also from vertical interpolations. These tests are also applied to a heat budget calculation involving nonlinear terms for one month. However, the latter comparison also brings in considerations of how best to do time averaging. Fortunately, in practical terms, differences between time-averaging approaches are quite small and probably negligible for most purposes. Other results show that truncation on model surfaces from T106 to T42 produces errors considerably larger than vertical interpolation errors. However, truncation to T63 for heat budget computations produces more acceptable, although not inconsequential, truncation errors provided that only T31 waves are retained as reasonably accurate.
Two potentially important papers by Wielicki et al. (1) and Chen et al. (2) dealt with aspects of how clouds and radiation vary and change, and whether climate models simulate the changes correctly. There is ample prior evidence suggesting that models have difficulties in correctly simulating clouds, and clouds are regarded as the biggest source of uncertainty in reports by the Intergovernmental Panel on Climate Change (IPCC) (3). However, an alternative interpretation of the disagreements shown between observations and models is that the analyses of the observations may be flawed.
No abstract is provided for this article.
No abstract is provided for this article.
Studies of the vertically-integrated energy and moisture budgets of the atmosphere are expanded to three dimensions. The vertical integrals of the moisture
No abstract is provided for this article.
Radiation is a fundamental variable for the whole flow of energy, and variations are perceived mainly by changes in cloudiness. Accordingly, the incoming and outgoing radiation are included here.
A perspective is given on human-induced climate change, contrasting two complementary approaches. The first is the conventional approach of using climate models as a means for developing understanding of the climate system variations and for projections of the future. Climate models have improved enormously, but even with the biggest supercomputers, models cannot resolve scales needed to depict many important phenomena. Major challenges remain in addressing chaotic natural weather and climate variability, and processing huge volumes of data. The second is an approach based upon understanding the changing Earth's energy imbalance (EEI) and tracking the consequences through the flows of energy through the climate system. A new assessment is given of the EEI through estimates of the uptake of heat by glaciers and ice sheets, land, and the oceans, and implications for the hydrological cycle. The oceans take up 93% of EEI of 0.9 ± 0.2 W m−2 (or 430 TW). Climate change is already readily apparent, with major consequences and costs.
