Our Planet:Climate Change and the Cryosphere, May 2007

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Similar model components exist to simulate the marine biosphere and chemistry. Integrated CO 2 emissions Boden et al. ESMs are also distinguished by the sophistication of their atmospheric and oceanic chemistry. In the ocean, biological productivity is limited by the availability of nutrients, ranging from fundamental cellular model components such as N to trace nutrients such as Fe, which is a key ingredient in many enzymes.

The distribution of these nutrients is controlled by transport and biology but also by reactions with dissolved organic matter and inorganic constituents. Nutrient cycling involving atmospheric transport is also important on land and can be affected by atmospheric chemical reactions. In addition, climate, as well as water and soil chemistry, can determine whether microbes decompose organic matter into methane or carbon dioxide.

Where are we going?

And once in the atmosphere, methane, a more efficient greenhouse gas, oxidizes to carbon dioxide, a less efficient greenhouse gas. Comparing an ESM with observations is not always straightforward. Observations are expensive to make and often limited in time and space. Even if they are available, they may have large uncertainties, or may be only indirectly related to what the model simulates. Fifty years ago, the vast majority of climate observations were of weather at the land surface in populated areas. Since that time, remote sensing of the Earth by instruments on artificial satellites and aircraft have expanded the type, spatial coverage, and frequency of climate observations.

These observations now are crucial to testing models. Translating the amount of radiation that the satellite observes to the appropriate model variable, however, often requires another model, adding uncertainty to the observations. Thus, both in situ directly measured and remote sensing data are necessary for comparison with models. Models are compared with observations at many different scales of time and space, and with as many types of observation as possible. Most model parameterizations are based on in situ experiments. Once included in an ESM, parameterizations are tuned to simulate current climate mean conditions as well as particular, well-observed events and their statistical distribution on longer timescales e.

Different model variables such as temperature, the amount of radiation observed at the top-of-atmosphere, ocean heat content, and greenhouse gas concentrations are all open to evaluation. To be considered credible, the individual model parameterizations and the full ESM must perform well on all these tests. Comparing the land carbon cycle model component of an ESM with observations could involve three types of test.

First, a process, such as the response of organic matter decomposition by soil microbes to changes in temperature and soil moisture, can be measured at an individual site. Second, satellite data can be used to study larger spatial scales than can be measured directly. For example, leaf area predicted in the model can be compared with satellite-observed values to see how well the model simulates the annual cycle of growth. Third, the model can be compared to longer-term compilations of data to see how it performs on decadal time scales and over large spatial scales.

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Since satellite data is limited to the last few decades, these compilations often mix satellite data with in situ measurements and economic data such as reports of lumber harvested from a nation's forests. The model's prediction of how much deforestation as well as reforestation has changed the carbon taken up by land over the past few decades can be compared to independent estimates based on atmospheric concentrations of carbon dioxide, carbon isotopes, and land-cover-change datasets. Another test of an ESM is the simulation of past climates paleoclimates. Projecting future climate change applies models tested against current conditions to new conditions and different concentrations of greenhouse gases and aerosols.

One way to feel more secure about these projections is to simulate paleoclimates. Paleoclimate data are collected from rock, ice, marine sediment, and lake sediment cores, as well as from other data sources such as tree rings and corals.

Studying and Projecting Climate Change with Earth System Models

This information usually has lower temporal and spatial resolution and larger uncertainties than current climate observations and often includes the use of proxies, which means that a variable of interest such as temperature is not directly measured; a variable the proxy that correlates well with the variable of interest is measured Instead.

ESM predictions differ for two reasons. First, models do not agree on the details of how climate, especially the distribution of precipitation, will change. Second, land carbon models are more or less sensitive to the four processes mentioned above. Further comparisons of these models with observational data will be necessary to reduce these uncertainties and suggest what improvements are needed. The cyclical process of model development and comparison with observations may seem circular.

It is more progressive than it appears. The changes in land carbon model sensitivity that resulted from adding a nitrogen cycle to simulate depletion of soil nutrients or including a strong response of microbial respiration to warming have motivated closer attention and more precise measurement of these processes. In these and other ways, ESMs have helped determine the answer to a critical question for us all: how the future of the Earth's climate will be shaped by the responses of its biosphere.

Boden, T. Cox, P. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature , , Friedlingstein, P.

References and Recommended Reading

Journal of Climate , 19 , Hansen, J. Target atmospheric CO 2 : Where should humanity aim? The Open Atmospheric Science Journal , 2 , Jouzel, J. Science , , Keeling, R. Kloster, S. Fire dynamics during the 20 th century simulated by the Community Land Model. Biogeosciences , 7 , Krishnamurthy, A.

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Lambert, F. Loulergue, L. Orbital and millennial-scale features of atmospheric CH 4 over the past , years. Luo, C. Combustion iron distribution and deposition. Global Biogeochemical Cycles , 22 , GB, doi High-resolution carbon dioxide concentration record ,, years before present. Mahowald, N. Change in atmospheric mineral aerosols in response to climate: Last glacial period, preindustrial, modern, and doubled carbon dioxide climates. Journal of Geophysical Research , , D Pope, V.

Testing and Evaluating Atmospheric Climate Models. Computing in Science and Engineering , 4 , Randall, D. Breaking the Cloud Parameterization Deadlock. Bulletin of the American Meteorological Society , 84 , Riley, W. Biogeosciences , 8 , , doi Sarmiento, J. Trends and regional distributions of land and ocean carbon sinks. Thornton, P. Influence of carbon-nitrogen cycle coupling on land model response to CO 2 fertilization and climate variability.

Global Biogeochemical Cycles , 21 , GB, doi Zeebe, R. Where are you heading Earth? Nature Geoscience , 4 , Modeling Sea Level Rise. The Global Climate System. Earth's Earliest Climate. Methane Hydrates and Contemporary Climate Change. Earth system models ESMs integrate the interactions of atmosphere, ocean, land, ice, and biosphere to estimate the state of regional and global climate under a wide variety of conditions.

Aa Aa Aa. A model organizes what we think we know about something in order to predict how it might behave in the present, future, or past as well as how it might respond to external influence.

Cryosphere | hiqukycona.tk

Models are especially useful when direct, controlled experiments are difficult or impossible. A model can be a simple concept, for instance: the heart is a circulating pump. A possible prediction from this model is that blood in the body regularly moves through the heart. Or a model can be a series of mathematical equations that are solved by computers.

Most scientists agree on two observations: mean global temperatures have risen at an increasing rate over the past several decades, and the amount of Earth's snow and ice cover has decreased over the same period.

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  • However, the cryosphere is also considered to be an early indicator of climate change, with melting glaciers, melting ice caps, and reduced snowfalls being signs of the impact of global warming. MEAN: A measure of central tendency average found by adding all the terms in a set and dividing by the number of terms. In our solar system , only Mars and Earth have polar ice caps. Earth's north polar ice cap has two parts, a skin of floating ice over the actual pole and the Greenland ice cap , which does not overlay the pole.

    Earth's south polar ice cap is the Antarctic ice sheet. The energy comes in many forms, such as visible light that which we can see with our eyes. Other forms of radiation include radio waves, heat infrared , ultraviolet waves, and x-rays. These forms are categorized within the electromagnetic spectrum. A major issue with the cryosphere is the high albedo of snow compared to land, and sea ice compared to the sea.

    On land, the high albedo reflective fraction of snow causes more solar radiation to be reflected from Earth.

    Without snow cover, more solar radiation is absorbed by land, and this enhances the warming effect. The same occurs for sea ice, where sea ice reflects more solar radiation than seawater. Without frozen sea ice present, a greater amount of radiation is absorbed and the warming effect is enhanced. This suggests that the cryosphere could play a role in accelerating global warming. Sea ice also impacts ocean circulation because it contains less salt than seawater, and its formation increases the salinity and density of surface water.

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    This density difference between surface water and deep water drives ocean circulation. With less sea ice forming, this ocean circulation could be reduced, which would then also influence the redistribution of heat. The cryosphere also plays a role in providing freshwater to regions throughout the world. Melting snow and melting glaciers are a major source of freshwater throughout Europe, North America , South America , and Asia.

    Reductions in snowfall and changes in the melting patterns of snow and glaciers could have a significant impact on global freshwater supplies.

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