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The Earth's climate has been continuously changing throughout its history. From ice covering large amounts of the globe to interglacial periods where there was ice only at the poles - our climate and biosphere has been in flux for millennia.

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This temporary reprieve from the ice we are now experiencing is called an interglacial period - the respite from the cold locker began 18,000 years ago as the earth started heating up and warming its way out of the Pleistocene Ice Age.

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Approximately every 100,000 years or so our climate warms up temporarily.

These interglacial periods usually last somewhere between 15,000 to 20,000 years before another ice age starts. Presently we're at year 18,000 of the current warm spell.

Serbian astrophysicist Milutin Milankovitch is best known for developing one of the most significant theories relating to Earths motions and long term climate change.

Milankovitch developed a mathematical theory of climate change based on the seasonal and latitudinal variations in the solar radiation received by the Earth from our Sun - it was the first truly plausible theory for how minor shifts of sunlight could make the entire planet's temperature swing back and forth from cold to warm.

Milankovitch's Theory states that as the Earth travels through space around the sun, cyclical variations in three elements of Earth/sun/geometry combine to produce variations in the amount of solar energy that reaches us. These three elements are:

• Variations in the Earth's orbital eccentricity - the shape of the orbit around the sun, a 100,000 year cycle
• Changes in obliquity or tilt of the earth's axis - changes in the angle that Earth's axis makes with the plane of Earth's orbit, a 41,000 year cycle
• Precession - the change in the direction of the Earth's axis of rotation, a 19,000 to 23,000 year cycle

These orbital processes are thought to be the most significant drivers of ice ages and, when combined, are known as Milankovitch Cycles.

Other Climate Change Drivers:

• Changes occurring within the sun affects the intensity of sunlight that reaches the Earth's surface. These changes in intensity can cause either warming - stronger solar intensity - or cooling when solar intensity is weaker.
• Volcanoes often affect our climate by emitting aerosols and carbon dioxide into the atmosphere. Aerosols block sunlight and contribute to short term cooling, but do not stay in the atmosphere long enough to produce long term change. Carbon dioxide (CO2) has a warming effect. For about two-thirds of the last 400 million years, geologic evidence suggests CO2 levels and temperatures were considerably higher than present. Each year 186 billion tons of carbon from CO2 enters the earth's atmosphere - six billion tons are from human activity, approximately 90 billion tons come from biologic activity in earth's oceans and another 90 billion tons from such sources as volcanoes and decaying land plants

These climate change "drivers" often trigger additional changes or "feedbacks" within the climate system that can amplify or dampen the climate's initial response to them:

• The heating or cooling of the Earth's surface can cause changes in greenhouse gas concentrations - when global temperatures become warmer, CO2 is released from the oceans and when temperatures become cooler, CO2 enters the ocean and contributes to additional cooling.

During at least the last 650,000 years, CO2 levels have tracked the glacial cycles - during warm interglacial periods, CO2 levels have been high and during cool glacial periods, CO2 levels have been low

• The heating or cooling of the Earth's surface can cause changes in ocean currents. Ocean currents play a significant role in distributing heat around the Earth so changes in these currents can bring about significant changes in climate from region to region

In 1985 the Russian Vostok Antarctic drill team pulled up cores of ice that stretched through a complete glacial cycle. During the cold period of the cycle CO2 levels were much lower than during the warm periods before and after. When plotted on a chart the curves of CO2 levels and temperature tracked one another very closely - methane, an even more potent greenhouse gas, showed a similar rise and fall to that of CO2.

Small rises or falls in temperature - more, or less sunlight - seemed to cause a rise, or fall, in gas levels. Changing atmospheric CO2 and methane levels physically linked the Northern and Southern hemispheres, warming or cooling the planet as a whole. In the 1980s the consensus was that Milankovitch's Cycles would bring a steady cooling over the next few thousand years.

As studies of past ice ages continued and climate models were improved worries about a near term re-entry into the cold locker died away - the models now said the next ice age would not come within the next ten thousand years.

It's obvious that the orbital changes, as explained by Milankovitch's Theory, initiate a powerful feedback loop. The close of a glacial era comes when a shift in sunlight causes a slight rise in temperature - this raises gas levels over the next few hundred years and the resultant greenhouse effect drives the planet's temperature higher, which drives a further rise in the gas levels and so on.

How Higher Temperatures effect Food Production

The study Climate Trends and Global Crop Production Since 1980 compared yield figures from the Food and Agriculture Organization (FAO) with average temperatures and precipitation in major growing regions.

Results indicated average global yields for several of the crops studied responded negatively to warmer temperatures. From 1981 - 2002, warming reduced the combined production of wheat, corn, and barley - cereal grains that form the foundation of much of the world's diet - by 40 million metric tons per year.

The authors said the main value of their study was that it demonstrated a clear and simple correlation between temperature increases and crop yields at the global scale.

"Though the impacts are relatively small compared to the technological yield gains over the same period, the results demonstrate that negative impacts are already occurring." David Lobell, lead researcher

Other researchers who focused on wheat, rice, corn, soybeans, barley and sorghum (these crops account for 55 percent of non-meat calories consumed by humans and contribute more than 70 percent of the world's animal feed) reported that each had a critical temperature threshold above which yields started plummeting, for example: 29°C for corn and 30°C for soybeans. At the International Rice Research Institute in the Philippines scientists have found that the fertilization of rice seeds falls from 100 per cent at 34 degrees to near zero at 40 degrees.

Crop losses due to plant diseases could decline by as much as 30 percent with warmer and drier conditions.

Demand

By 2050, the world's population is expected to reach around nine billion - minimum and maximum projections range from 7.4 billion to 10.6 billion.

Unfortunately the Green Revolutions high yield growth is tapering off and in some cases declining. So far this is mostly because of an increase in the price of fertilizers, other chemicals and fossil fuels, but also because the overuse of chemicals has exhausted the soil and irrigation has depleted water aquifers.

Yield

"Future food-production increases will have to come from higher yields. And though I have no doubt yields will keep going up, whether they can go up enough to feed the population monster is another matter. Unless progress with agricultural yields remains very strong, the next century will experience sheer human misery that, on a numerical scale, will exceed the worst of everything that has come before". Norman Borlaug, father of the Green Revolution

If average global temperatures rise just over one-half degree Centigrade the frost-free growing season in the corn belt would be lengthened by two weeks. But, as the previously mentioned study showed, if temperatures increase beyond a specific threshold, fertilization is effected, thus reducing the plants growing season and reducing yield.

Carbon dioxide does two things for plants - it is an essential compound in photosynthesis and it increases water use efficiency in plants - so a doubling of the pre-industrial carbon-dioxide levels, such as we've seen, should increase crop yields significantly right?

Well let's not jump to conclusions - in laboratory tests yields do increase tremendously, but in real life field conditions other atmospheric gases surrounding the plant diminish the carbon dioxide's photosynthesis enhancement and yield levels reached in the lab are cut drastically, as much as 75 percent.

All of the positive effects of carbon dioxide increases may be negated by the stress caused by low rainfall and high temperatures. Increased cloud cover - due to higher global temperatures - might limit photosynthesis and result in reduced crop production.

Higher levels of carbon dioxide help some plants tolerate less water and limited amounts of soil nitrogen but does not compensate for reduced levels of phosphorus or potassium.

If global warming raises the temperature just two degrees Centigrade insects numbers will increase becoming a major nuisance - also some insects will be able to extend their range as a result of the warming. Farmers in the US, depending on the crop, can expect a 25 to 100 percent increase in crop losses.

Conclusion

The heating and cooling of the Earth coincides with the activity of the sun - the sun determines the Earth's temperature. Since man-made carbon dioxide emissions started in the 1850's, the CO2 level has only risen 11 percent - a very small rise with a nearly negligible effect.

Science says the Earth is going to continue to warm. The warming is not manmade, to continue to spend precious resources fighting a battle you cannot win is a fruitless endeavor. The earth is our home and we need to take care of it best we can, there is no gain needlessly hurting the planet we live on. But let's not be led astray by false prophets and Pied Pipers singing the wrong tune. We need to spend money on advancing agricultural research, water infrastructure and supply lines. We need to focus research on growing more food on less land while using less water and building safe, reliable food and water supply lines.

The truth regarding climate change, and how it effects our food production should be on all our radar screens. Is it on yours?

If not, maybe it should be.