Climate Change

Posted by on gen 22, 2014 in Sustainability Mission | 0 comments

Climate Change

Human Effects on Climate

Human activities are continuing to affect the Earth’s energy budget by changing the emissions and resulting atmospheric concentrations of radiatively important gases and aerosols and by changing land surface properties. Previous assessments have already shown through multiple lines of evidence that the climate is changing across our planet, largely as a result of human activities. The most compelling evidence of climate change derives from observations of the atmosphere, land, oceans, and cryosphere.

Unequivocal evidence from in situ observations and ice core records shows that the atmospheric concentrations of important greenhouse gases such as carbon dioxide, methane, and nitrous oxides have increased over the last few centuries.

The processes affecting climate can exhibit considerable natural variability. Even in the absence of external forcing, periodic and chaotic variations on a vast range of spatial and temporal scales are observed. Much of this variability can be represented by simple (e.g., unimodal or power law) distributions, but many components of the climate system also exhibit multiple states – for instance, the glacial-interglacial cycles and certain modes of internal variability such as El Niño-Southern Oscillation (ENSO). Movement between states can occur as a result of natural variability, or in response to external forcing. The relationship between variability, forcing and response reveals the complexity of the dynamics of the climate system: the
relationship between forcing and response for some parts of the system seems reasonably linear; in other cases this relationship is much more complex.

Multiple Lines of Evidence for Climate Change 

Global mean surface air temperatures over land and oceans have increased over the last 100 years. The temperature measurements in the oceans show a continuing increase in the heat content of the oceans. Analyses based on measurements of the Earth’s radiative budget suggest a small positive energy imbalance that serves to increase the global heat content of the Earth system. Observations from satellites and in situ measurements show a trend of significant reductions in the mass balance of most land ice masses and in Arctic sea ice. The ocean’s uptake of carbon dioxide is having a significant effect on the chemistry of sea water. Paleoclimatic reconstructions have helped place ongoing climate change in the perspective of natural
climate variability.

Observations of carbon dioxide (CO2) concentrations, globally-averaged temperature and sea level rise are generally well within the range of the extent of the earlier IPCC projections. The recently observed increases in methane (CH4) and nitrous oxide (N2O) concentrations are smaller than those assumed in the scenarios in the previous assessments. Each IPCC assessment has used new projections of future climate change that have become more detailed as the models have become more advanced. Similarly, the scenarios themselves used in the IPCC assessments have changed over time to reflect the state of knowledge. The range of climate projections from model results provided and assessed in the first IPCC assessment in
1990 to those in the 2007 AR4 provides an opportunity to compare the projections with the actually observed changes, thereby examining the deviations of the projections from the observations over time.

Climate change, whether driven by natural or human forcing, can lead to changes in the likelihood of the occurrence or strength of extreme weather and climate events or both. Since the AR4, the observational basis has increased substantially, so that some extremes are now examined over most land areas. Furthermore, more models with higher resolution and more regional models have been used in the simulations and projections of extremes.


Source: Climate Change 2013: The Physical Science Basis – IPCC
Read the full paper here

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