PubMed Health⌕ Search

Biomedical subjects

James Hansen

Publications and source records attributed to James Hansen.

10 recordsLinked to original sources
PubMed2006

Global temperature change.

Global surface temperature has increased approximately 0.2 degrees C per decade in the past 30 years, similar to the warming rate predicted in the 1980s in initial global climate model simulations with transient greenhouse gas changes. Warming is larger in the Western Equatorial Pacific than in the Eastern Equatorial Pacific over the past century, and we suggest that the increased West-East temperature gradient may have increased the likelihood of strong El Niños, such as those of 1983 and 1998. Comparison of measured sea surface temperatures in the Western Pacific with paleoclimate data suggests that this critical ocean region, and probably the planet as a whole, is approximately as warm now as at the Holocene maximum and within approximately 1 degrees C of the maximum temperature of the past million years. We conclude that global warming of more than approximately 1 degrees C, relative to 2000, will constitute "dangerous" climate change as judged from likely effects on sea level and extermination of species.

Greenhouse Effect↗
PubMed2006

Sex-related dimorphic response of HIF-1 alpha expression in myocardial ischemia.

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) plays a role in a number of cell-protective pathways after ischemia. There are clear sex-related differences in the remodeling process, and hearts from males tend to dilate in response to pathological loads and ischemia to a greater degree than do hearts from females. Thus we hypothesized that there would be a sex-related dimorphic response of HIF-1 alpha to an ischemic event. Male and female rats were euthanized 5 and 24 h after coronary ligation (M-MI and F-MI; MI, myocardial ischemia), and HIF-1 alpha expression was determined by immunohistochemistry, Western blot, and quantitative RT-PCR. Sham-operated male and female animals served as controls (M-SH and F-SH). In the ischemic area, histochemical analysis at 5 h showed that HIF was expressed in 33% of cell nuclei in M-MI and in 55% in F-MI. At 24 h, HIF expression increased to 49% in M-MI and to 82% in F-MI (P < 0.05 vs. SH and also M-MI vs. F-MI). This difference was not only statistically significant between the two sexes at 24 h but also within each sex at 5 and 24 h after ligation. Western blots confirmed that, at 24 h after ischemia, HIF protein increased significantly in both male and female hearts relative to sham-operated animals but that the increase in females was 60% greater than that seen in males. mRNA expression of HIF was significantly increased at 24 h in F-MI versus M-MI and sham-operated animals. Expression of downstream HIF target genes (heme oxygenase and brain natriuretic peptide) was increased in proportion to the levels of HIF expression. These data suggest a novel cellular mechanism to explain the sex-related dimorphic response to ischemia and also the possibility that exogenous modulation of HIF might represent a new therapeutic approach to preventing left ventricular remodeling.

Animals↗
PubMed2005

Earth's energy imbalance: confirmation and implications.

Our climate model, driven mainly by increasing human-made greenhouse gases and aerosols, among other forcings, calculates that Earth is now absorbing 0.85 +/- 0.15 watts per square meter more energy from the Sun than it is emitting to space. This imbalance is confirmed by precise measurements of increasing ocean heat content over the past 10 years. Implications include (i) the expectation of additional global warming of about 0.6 degrees C without further change of atmospheric composition; (ii) the confirmation of the climate system's lag in responding to forcings, implying the need for anticipatory actions to avoid any specified level of climate change; and (iii) the likelihood of acceleration of ice sheet disintegration and sea level rise.

Journal Article↗
PubMed2005

Associating ecosystem service losses with indicators of toxicity in habitat equivalency analysis.

Habitat equivalency analysis (HEA) was developed as a tool to scale mitigation or restoration when habitat is contaminated by hazardous substances or has been otherwise harmed by anthropogenic activities. Applying HEA involves balancing reductions in habitat quality against gains from restoration actions, and quantifying changes in habitat quality in terms of ecological services. We propose a framework for developing ecological service definitions and measures that incorporate knowledge about the impacts of chemical contaminants on biota. We describe a general model for integrating multiple lines of evidence about the toxicity of hazardous substances to allow mapping of toxicological inputs to ecological service losses. We provide an example of how this framework might be used in a HEA that quantifies ecological services provided by estuarine sediments contaminated with polycyclic aromatic hydrocarbons.

Ecology↗
PubMed2004

Greenhouse gas growth rates.

We posit that feasible reversal of the growth of atmospheric CH(4) and other trace gases would provide a vital contribution toward averting dangerous anthropogenic interference with global climate. Such trace gas reductions may allow stabilization of atmospheric CO(2) at an achievable level of anthropogenic CO(2) emissions, even if the added global warming constituting dangerous anthropogenic interference is as small as 1 degrees C. A 1 degrees C limit on global warming, with canonical climate sensitivity, requires peak CO(2) approximately 440 ppm if further non-CO(2) forcing is +0.5 W/m(2), but peak CO(2) approximately 520 ppm if further non-CO(2) forcing is -0.5 W/m(2). The practical result is that a decline of non-CO(2) forcings allows climate forcing to be stabilized with a significantly higher transient level of CO(2) emissions. Increased "natural" emissions of CO(2), N(2)O, and CH(4) are expected in response to global warming. These emissions, an indirect effect of all climate forcings, are small compared with human-made climate forcing and occur on a time scale of a few centuries, but they tend to aggravate the task of stabilizing atmospheric composition.

Journal Article↗
PubMed2003

Soot climate forcing via snow and ice albedos.

Plausible estimates for the effect of soot on snow and ice albedos (1.5% in the Arctic and 3% in Northern Hemisphere land areas) yield a climate forcing of +0.3 W/m(2) in the Northern Hemisphere. The "efficacy" of this forcing is approximately 2, i.e., for a given forcing it is twice as effective as CO(2) in altering global surface air temperature. This indirect soot forcing may have contributed to global warming of the past century, including the trend toward early springs in the Northern Hemisphere, thinning Arctic sea ice, and melting land ice and permafrost. If, as we suggest, melting ice and sea level rise define the level of dangerous anthropogenic interference with the climate system, then reducing soot emissions, thus restoring snow albedos to pristine high values, would have the double benefit of reducing global warming and raising the global temperature level at which dangerous anthropogenic interference occurs. However, soot contributions to climate change do not alter the conclusion that anthropogenic greenhouse gases have been the main cause of recent global warming and will be the predominant climate forcing in the future.

Journal Article↗
PubMed2003

Global atmospheric black carbon inferred from AERONET.

AERONET, a network of well calibrated sunphotometers, provides data on aerosol optical depth and absorption optical depth at >250 sites around the world. The spectral range of AERONET allows discrimination between constituents that absorb most strongly in the UV region, such as soil dust and organic carbon, and the more ubiquitously absorbing black carbon (BC). AERONET locations, primarily continental, are not representative of the global mean, but they can be used to calibrate global aerosol climatologies produced by tracer transport models. We find that the amount of BC in current climatologies must be increased by a factor of 2-4 to yield best agreement with AERONET, in the approximation in which BC is externally mixed with other aerosols. The inferred climate forcing by BC, regardless of whether it is internally or externally mixed, is approximately 1 W/m2, most of which is probably anthropogenic. This positive forcing (warming) by BC must substantially counterbalance cooling by anthropogenic reflective aerosols. Thus, especially if reflective aerosols such as sulfates are reduced, it is important to reduce BC to minimize global warming.

Journal Article↗
PubMed2002

Changing trends in sulfur emissions in Asia: implications for acid deposition, air pollution, and climate.

In the early 1990s, it was projected that annual SO2 emissions in Asia might grow to 80-110 Tg yr(-1) by 2020. Based on new high-resolution estimates from 1975 to 2000, we calculate that SO2 emissions in Asia might grow only to 40-45 Tg yr(-1) by 2020. The main reason for this lower estimate is a decline of SO2 emissions from 1995 to 2000 in China, which emits about two-thirds of Asian SO2. The decline was due to a reduction in industrial coal use, a slowdown of the Chinese economy, and the closure of small and inefficient plants, among other reasons. One effect of the reduction in SO2 emissions in China has been a reduction in acid deposition not only in China but also in Japan. Reductions should also improve visibility and reduce health problems. SO2 emission reductions may increase global warming, but this warming effect could be partially offset by reductions in the emissions of black carbon. How SO2 emissions in the region change in the coming decades will depend on many competing factors (economic growth, pollution control laws, etc.). However a continuation of current trends would result in sulfur emissions lower than any IPCC forecasts.

Acid Rain↗
PubMed2002

Climate effects of black carbon aerosols in China and India.

In recent decades, there has been a tendency toward increased summer floods in south China, increased drought in north China, and moderate cooling in China and India while most of the world has been warming. We used a global climate model to investigate possible aerosol contributions to these trends. We found precipitation and temperature changes in the model that were comparable to those observed if the aerosols included a large proportion of absorbing black carbon ("soot"), similar to observed amounts. Absorbing aerosols heat the air, alter regional atmospheric stability and vertical motions, and affect the large-scale circulation and hydrologic cycle with significant regional climate effects.

Journal Article↗