Kevin E. Trenberth emphasizes the fundamental role of energy flows in the climate system and anthropogenic climate change. The distribution of heat, or more generally, energy, is the main determinant of weather patterns in the atmosphere and their impacts. The topics addressed cover many facets of climate and the climate crisis. These include the diurnal cycle; the seasons; energy differences between the continents and the oceans, the poles and the tropics; interannual variability such as Nino; natural decadal variability; and ice ages. Human-induced climate change rides on and interacts with all of these natural phenomena, and the result is an unevenly warming planet and changing weather extremes. The book emphasizes the need to not only slow or stop climate change, but also to better prepare for it and build resilience. Students, researchers, and professionals from a wide range of backgrounds will benefit from this deeper understanding of climate change.
To assess climate sensitivity from Earth radiation observations of limited duration and observed sea surface temperatures (SSTs) requires a closed and therefore global domain, equilibrium between the fields, and robust methods of dealing with noise. Noise arises from natural variability in the atmosphere and observational noise in precessing satellite observations. This paper explores the meaning of results that use only the tropical region. We compute correlations and regressions between tropical SSTs and top‐of‐atmosphere (TOA) longwave, shortwave and net radiation using a variety of methods to test robustness of results. The main changes in SSTs throughout the tropics are associated with El Niño Southern Oscillation (ENSO) events in which the dominant changes in energy into an atmospheric column come from ocean heat exchange through evaporation, latent heat release in precipitation, and redistribution of that heat through atmospheric winds. These changes can be an order of magnitude larger than the net TOA radiation changes, and their effects are teleconnected globally, and especially into the subtropics. Atmospheric model results are explored and found to be consistent with observations. From 1985 to 1999 the largest perturbation in TOA radiative fluxes was from the eruption of Mount Pinatubo and clearly models which do not include that forcing will not simulate the effects. Consequently, regressions of radiation with SSTs in the tropics may have nothing to say about climate sensitivity.
Stationary planetary waves forced by orography and diabatic beating are studied using a quasi-geostrophic two-level model on a beta-plane. This study extends a previous one by Trenberth to include the effects of a baroclinic atmosphere with zonal mean wind shear. With the introduction of vertical shear, the temperature field is no longer locked onto the heating field and can become orthogonal so that even though the wave is thermally forced there may not be any generation or loss of energy by diabatic heating. The presence of both thermal and orographic forcing together violates the conditions of nonacceleration of the zonal mean flow. The induced changes in the zonal mean flow strongly depend upon the relative phase of the thermal and orographic forcing. With a specified diabatic heating field, the eddy fluxes and changes of zonal mean flow are not sensitive to the strength of the mean zonal wind shear. By increasing the wind shear, however, the vertically propagating waves become trapped. The trapped waves accelerate the zonal mean flow through an induced meridional circulation distinct from that of the propagating waves. The characteristics of the forced waves can be explained by the local index of refraction. Results indicating important differences between the stationary planetary waves in the two hemispheres are 1) the higher total wave number in the Southern Hemisphere, which arises from the shorter meridional scale, so that the waves are trapped, and 2) interaction between thermal and orographic waves in the Northern Hemisphere which is less likely in the Southern Hemisphere. The limitations of the two-level model with the traditional fixed upper boundary condition, ω = 0 at p = 0, in reproducing forced planetary waves is evaluated by testing the sensitivity of results to a modified radiation upper boundary condition. Distinct differences are found when the planetary waves can propagate vertically. Not only is the response of the planetary waves different in phase and magnitude but also the induced acceleration of the zonal mean flow can be completely opposite. Nevertheless, there is reasonable agreement when the planetary waves are trapped vertically so that the upper boundary conditions have minor impact.
A reappraisal of the messy data on upper-ocean heat content for 1993–2008 provides clear evidence for warming. But differences among various analyses and inconsistencies with other indicators merit attention. The upper ocean acts as a giant heat sink and has absorbed the majority of excess energy generated by anthropogenic greenhouse gasses. This makes ocean heat content, potentially, a key indicator of climate change. But to be useful for evaluating the global energy balance and as a constraint on climate models, the measurement uncertainties of such a key indicator need to be well understood. At present the magnitude of the oceanic heat uptake is highly uncertain, with patterns of inter-annual variability in particular differing among estimates. In a major international collaboration, Lyman et al. compare the available upper-ocean heat content anomaly curves and examine the sources of uncertainly attached to them — including the difficulties in correcting bias in expendable bathythermograph data. They find that, uncertainties notwithstanding, there is clear and robust evidence for a warming trend of 0.64 watts per square metre between 1993 and 2008.
No abstract is provided for this article.
This report reflects the discussions and recommendations of Breakout Group B. It is recognized that there are gaps and imbalances in the topics covered. These came about from the particular expertise of the collection of scientists who happened to be present and the...
A short nontechnical review of the El Niño–Southern Oscillation (ENSO) phenomenon and the associated teleconnections to higher latitudes is given. ENSO has been shown to be predictable to some degree for over a year ahead, which therefore provides a basis for skillful prediction of interannual variations in climate. The processes involved are emphasized in order to highlight the areas where future research may most profitably be directed to improve climate forecasts. This progress has been realized through the successful completion of the Tropical Oceans Global Atmosphere (TOGA) Program of the World Climate Research Program (WCRP), which has established and maintained the TOGA Observing System, developed coupled atmosphere–ocean models of the tropical Pacific Ocean, demonstrated the predictive capabilities noted above, and conducted field programs to further the understanding of physical processes. Future research will take place in the context of a developing infrastructure associated with operational climate forecasts. Short-term climate variability involves much more than ENSO, and the challenge is to also capitalize on long timescales associated with anomalies in other parts of the climate system and any additional predictability that goes beyond simple persistence and build this into any prediction scheme. The international framework for helping to facilitate future research is CLIVAR–GOALS, the WCRP program on climate variability and predictability, and the subprogram on the Global Ocean–Atmosphere–Land System. The research challenges are many, but the prospects are excellent for making further advances and the potential is high for socioeconomic benefits for many countries. Turning skillful but uncertain forecasts into useful information and beneficial decisions represents a particular challenge, so that collaboration will be required between the physical scientists and scientists from the applications and social science communities.
<title>Abstract</title> <bold>Huge heat anomalies in the past few years are not explained by climate models</bold><sup><bold>1</bold></sup><bold>. Strong characteristic patterns in temperatures for upper layers of the ocean occurred from 2000 to 2023 in the presence of global warming from increasing atmospheric greenhouse gases</bold><sup><bold>2</bold></sup><bold>. Here we show that the deep tropics are warming, although sharply modulated by El Niño-Southern Oscillation events, with strong heating in the extratropics near 40°N and 40 to 45°S, but little heating near 20°N and 25-30°S. The heating is most clearly manifested in zonal mean ocean heat content and is evident in sea surface temperatures. Strongest heating is in the Southern Hemisphere, where aerosol effects are small. Estimates are made of the contributions of top-of-atmosphere (TOA) radiation, atmospheric energy transports, surface fluxes of energy, and redistribution of energy by surface winds and ocean currents. The patterns are not directly related to TOA radiation but are strongly evident in net surface energy fluxes. Changes in the atmospheric circulation, jet streams, and storm tracks are reflected in surface ocean Ekman transports. As well as climate change, natural variability is likely in play. Hence the atmosphere and ocean currents are systematically redistributing heat from global warming, profoundly affecting local climates.</bold>
No abstract is provided for this article.
No abstract is provided for this article.
Current human-induced climate change arises primarily from the heating of the planet mainly from changes in atmospheric composition, and temperature change is one manifestation. The increasing greenhouse gases, notably carbon dioxide from burning fossil fuels, lead to Earth’s Energy Imbalance (EEI), altering the flow of energy through the climate system, and the dissemination of excess energy is partly what determines how climate change is manifested. Some of the extremes being experienced, especially those involving drought, convection, storms, flooding, and the water cycle, are mostly driven by aspects of heating and, while temperature contributes through the water-holding capacity of the atmosphere, it is more a consequence than a cause. Afterall, water is the air conditioner of the planet. The United Nations, and especially the Intergovernmental Panel on Climate Change (IPCC) in their Summary for Policy Makers, focus on global temperature targets rather than broader facets of climate change including EEI, and do not always adequately discriminate between temperature and heating. This also has consequences for future climate if or when heating is brought under control by cutting emissions. Improvements are needed in expressing how the climate is changing by properly accounting for the flow of energy through the climate system.
Broad vertical layer-averaged temperatures from the microwave sounder unit (MSU) are used as a quasi-independent validation of temperature fields from the U.S. National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses. While the MSU and NCEP–NCAR temperatures show fairly good agreement overall, large discrepancies with ECMWF temperatures indicate that changes in the satellite observing system may have adversely affected the ECMWF reanalyses, especially in the Tropics. Two spurious discontinuities are present in tropical temperatures with jumps to warmer values throughout the Tropics below 500 mb in late 1986 and early 1989, and further spurious interannual variability is also present. These features are also reflected in the specific humidity fields. The temperature discrepancies have a complex vertical structure with height that is not fully understood, although it seems that the problems partly arise from positive reinforcement of biases in satellite radiances with those of the assimilating model first guess. Changes in the observing system provide a limit to the usefulness of the reanalyses in some climate studies.
No abstract is provided for this article.
No abstract is provided for this article.
Earth's energy imbalance (EEI) drives the ongoing global warming and can best be assessed across the historical record (that is, since 1960) from ocean heat content (OHC) changes. An accurate assessment of OHC is a challenge, mainly because of insufficient and irregular data coverage. We provide updated OHC estimates with the goal of minimizing associated sampling error. We performed a subsample test, in which subsets of data during the data-rich Argo era are colocated with locations of earlier ocean observations, to quantify this error. Our results provide a new OHC estimate with an unbiased mean sampling error and with variability on decadal and multidecadal time scales (signal) that can be reliably distinguished from sampling error (noise) with signal-to-noise ratios higher than 3. The inferred integrated EEI is greater than that reported in previous assessments and is consistent with a reconstruction of the radiative imbalance at the top of atmosphere starting in 1985. We found that changes in OHC are relatively small before about 1980; since then, OHC has increased fairly steadily and, since 1990, has increasingly involved deeper layers of the ocean. In addition, OHC changes in six major oceans are reliable on decadal time scales. All ocean basins examined have experienced significant warming since 1998, with the greatest warming in the southern oceans, the tropical/subtropical Pacific Ocean, and the tropical/subtropical Atlantic Ocean. This new look at OHC and EEI changes over time provides greater confidence than previously possible, and the data sets produced are a valuable resource for further study.
