Engineering topics

Hansen, James

Publications and source records attributed to Hansen, James.

31 records · Page 2

NASA NTRS2012

Public Perception of Climate Change and the New Climate Dice

"Climate dice", describing the chance of unusually warm or cool seasons, have become more and more "loaded" in the past 30 years, coincident with rapid global warming. The distribution of seasonal mean temperature anomalies has shifted toward higher temperatures and the range of anomalies has increased. An important change is the emergence of a category of summertime extremely hot outliers, more than three standard deviations (3 sigma) warmer than the climatology of the 1951-1980 base period. This hot extreme, which covered much less than 1% of Earth's surface during the base period, now typically covers about 10% of the land area. It follows that we can state, with a high degree of confidence, that extreme anomalies such as those in Texas and Oklahoma in 2011 and Moscow in 2010 were a consequence of global warming, because their likelihood in the absence of global warming was exceedingly small. We discuss practical implications of this substantial, growing, climate change.

Hansen, James↗

NASA NTRS2002

The Temperature of the Earth in 2020

In spite of the confusion in the public discourse about global warming, there is no doubt that the Earth has been warming for the past century. The chemistry of the Earth's atmosphere is complex, and it is sometimes difficult to claim cause-and-effect with certainty. Nevertheless, the evidence seems clear that CO2 and non-CO2 forcings such as methane and air pollution are causally related to this warming trend. Our dependence on fossil fuels make it difficult to expect that massive reductions in CO2 will be feasible in the near-term, however. In this talk I will consider the evidence for global warming, the extent to which we can extrapolate current trends into the future if no changes in global policy are introduced, and those near-term policies that might be realistically introduced to significantly affect those trends.

Hansen, James↗

NASA NTRS2001

The NASA Seasonal-to-Interannual Prediction Project (NSIPP)

The goal of the project is to develop an assimilation and forecast system based on a coupled atmosphere-ocean-land-surface-sea-ice model capable of using a combination of satellite and in situ data sources to improve the prediction of ENSO and other major S-I signals and their global teleconnections. The objectives of this annual report are to: (1) demonstrate the utility of satellite data, especially surface height surface winds, air-sea fluxes and soil moisture, in a coupled model prediction system; and (2) aid in the design of the observing system for short-term climate prediction by conducting OSSE's and predictability studies.

Rienecker, Michele↗

NASA NTRS2000

Global Warming in the Twenty-First Century: An Alternative Scenario

A common view is that the current global warming rate will continue or accelerate. But we argue that rapid warming in recent decades has been driven mainly by non-CO2 greenhouse gases (GHGs), such as chlorofluorocarbons, CH4, and N2O, not by the products of fossil fuel burning, CO2 and aerosols, the positive and negative climate forcings of which are partially offsetting. The growth rate of non-CO2 GHGs has declined in the past decade. If sources of CH4 and O3 precursors were reduced in the future, the change in climate forcing by non-CO2 GHGs in the next 50 years could be near zero. Combined with a reduction of black carbon emissions and plausible success in slowing CO2 emissions, this reduction of non-CO2 GHGs could lead to a decline in the rate of global warming, reducing the danger of dramatic climate change. Such a focus on air pollution has practical benefits that unite the interests of developed and developing countries. However, assessment of ongoing and future climate change requires composition specific long-term global monitoring of aerosol properties.

Hansen, James↗

NASA NTRS2000

Global Warming in the Twenty-First Century: An Alternative Scenario

Hansen, James↗

NASA NTRS2000

Contribution of Changing Sources and Sinks to the Growth Rate of Atmospheric Methane Concentrations for the Last Two Decades

In situ measurements of atmospheric methane concentrations begun in the early 1980s show decadal trends, as well as large interannual variations, in growth rate. Recent research indicates that while wetlands can explain several of the large growth anomalies for individual years, the decadal trend may be the combined effect of increasing sinks, due to increases in tropospheric OH, and stabilizing sources. We discuss new 20-year histories of annual, global source strengths for all major methane sources, i.e., natural wetlands, rice cultivation, ruminant animals, landfills, fossil fuels, and biomass burning, and present estimates of the temporal pattern of the sink required to reconcile these sources and atmospheric concentrations over the time period. Analysis of the individual emission sources, together with model-derived estimates of the OH sink strength, indicates that the growth rate of atmospheric methane observed over the last 20 years can only be explained by a combination of changes in source emissions and an increasing tropospheric sink.

Matthews, Elaine↗

NASA NTRS1993

Climate forcings and feedbacks

Global temperature has increased significantly during the past century. Understanding the causes of observed global temperature change is impossible in the absence of adequate monitoring of changes in global climate forcings and radiative feedbacks. Climate forcings are changes imposed on the planet's energy balance, such as change of incoming sunlight or a human-induced change of surface properties due to deforestation. Radiative feedbacks are radiative changes induced by climate change, such as alteration of cloud properties or the extent of sea ice. Monitoring of global climate forcings and feedbacks, if sufficiently precise and long-term, can provide a very strong constraint on interpretation of observed temperature change. Such monitoring is essential to eliminate uncertainties about the relative importance of various climate change mechanisms including tropospheric sulfate aerosols from burning of coal and oil smoke from slash and burn agriculture, changes of solar irradiance changes of several greenhouse gases, and many other mechanisms. The considerable variability of observed temperature, together with evidence that a substantial portion of this variability is unforced indicates that observations of climate forcings and feedbacks must be continued for decades. Since the climate system responds to the time integral of the forcing, a further requirement is that the observations be carried out continuously. However, precise observations of forcings and feedbacks will also be able to provide valuable conclusions on shorter time scales. For example, knowledge of the climate forcing by increasing CFC's relative to the forcing by changing ozone is important to policymakers, as is information on the forcing by CO2 relative to the forcing by sulfate aerosols. It will also be possible to obtain valuable tests of climate models on short time scales, if there is precise monitoring of all forcings and feedbacks during and after events such as a large volcanic eruption or an El Nino.

Hansen, James↗

NASA NTRS1993

Climsat rationale

We summarize reasons for the Climsat proposition; we also stress the need for certain climate monitoring other than that supplied by Climsat, especially solar irradiance, and we stress the complementarity of Climsat monitoring to plans for detailed EOS measurements. Existing and planned observations will not provide measurements of most climate forcing and feedback parameters with the accuracy needed to measure plausible decadal changes. Stratospheric water vapor and aerosol requirements are not met, for example, even though the present SAGE II instrument on the ERBS spacecraft measures those two parameters accurately, because ERBS is not expected to last more than a few years and it does not provide global coverage. We stress the imminence of a potential data gap even of those parameters, such as solar irradiance and stratospheric aerosols, for which monitoring capability has been proven and currently is in place. We find that most of the missing global climate forcings and feedbacks can be measured by three small instruments, which would need to be deployed on two spacecraft to obtain adequate sampling and global coverage. The monitoring must be maintained continuously for at least two decades. Such continuity can be attained by replacing a satellite after it fails, the functioning satellite providing calibration transfer to the new satellite. Certain complementary monitoring data are also needed, including solar monitoring from space, in order to fully meet requirements for monitoring all the climate forcings and feedbacks. The complementary data needs are discussed toward the end of this section. We summarize the proposed Climsat measurements and compare the expected accuracies to those which are needed to analyze changes of the global thermal energy cycle on decadal time scales. We stress the need to get broader participation of the scientific community in the monitoring and analysis activity. Finally, we discuss related climate process and diagnostic measurements.

Hansen, James↗

NASA NTRS1992

Climate forcing by stratospheric aerosols

It is illustrated how climate forcing by stratospheric aerosols depends on aerosol properties. The climate forcing is a function of aerosols size distribution, but the size dependence can be described well by a single parameter: the area-weighted mean radius, r(eff). If r(eff) is greater than about 2 microns, the global average greenhouse effect of the aerosols exceeds the albedo effect, causing a surface heating. The aerosol climate forcing is less sensitive to other characteristics of the size distribution, the aerosol composition, and the altitude of the aerosols. Thus stratospheric aerosol forcing can be defined accurately from measurements of aerosol extinction over a broad wavelength range.

Lacis, Andrew↗

NASA NTRS1992

Potential climate impact of Mount Pinatubo eruption

The GISS global-climate model is used to make a preliminary estimate of Mount Pinatubo's climate impact. Assuming the aerosol optical depth is nearly twice as great as for the 1982 El Chichon eruption, the model forecasts a dramatic but temporary break in recent global warming trends. The simulations indicate that Pinatubo occurred too late in the year to prevent 1991 from becoming one of the warmest years in instrumental records, but intense aerosol cooling is predicted to begin late in 1991 and to maximize late in 1992. The predicted cooling is sufficiently large that by mid 1992 it should even overwhelm global warming associated with an El Nino that appears to be developing, but the El Nino could shift the time of minimum global temperature into 1993. The model predicts a return to record warm levels in the later 1990s. The effect is estimated of the predicted global cooling on such practical matters as the severity of the coming Soviet winter and the dates of cherry blossoming next spring.

Hansen, James↗

NASA NTRS1989

Greenhouse effect of chlorofluorocarbons and other trace gases

A comparison is made of the radiative (greenhouse) forcing of the climate system due to changes of atmospheric chlorofluorocarbons and other trace gases. It is found that CFCs, defined to include chlorofluorocarbons, chlorocarbons, and fluorocarbons, now provide about one-quater of current annual increases in anthropogenic greenhouse climate forcing. If the growth rates of CFC production in the early 1970s had continued to the present, current annual growth of climate forcing due to CFCs would exceed that due to CO2.

Hansen, James↗

NASA NTRS1988

Global surface air temperatures - Update through 1987

Data from meteorological stations show that surface air temperatures in the 1980s are the warmest in the history of instrumental records. The four warmest years on record are all in the 1980s, with the warmest years in the analysis being 1981 and 1987. The rate of warming between the mid-1960s and the present is higher than that which occurrred in the previous period of rapid warming between the 1880s and 1940.

Hansen, James↗

NASA NTRS1987

Global trends of measured surface air temperature

The paper presents the results of surface air temperature measurements from available meteorological stations for the period of 1880-1985. It is shown that the network of meteorological stations is sufficient to yield reliable long-term, decadal, and interannual temperature changes for both the Northern Hemisphere and the Southern Hemisphere, despite the fact that most stations are located on the continents. The results indicate a global warming of about 0.5-0.7 C in the past century, with warming of similar magnitude in both hemispheres. A strong warming trend between 1965 and 1980 raised the global mean temperature in 1980 and 1981 to the highest level in the period of instrumental records. Selected graphs of the temperature change in each of the eight latitude zones are included.

Hansen, James↗