climate+change

Climate change is probably one of the most controversial, yet most profoundly important, topics of today's modern society. Its potential to impact the future of human civilization, and the ecology of the planet as we know it, makes it an extensively debated topic.

There should be no doubt, based on the data collected by scientists around the world over the past century, that there are changes occurring in Earth's climate. The evidence of these changes will be summarized here. The debate is focused mainly on whether or not these changes are man-made, or are part of the natural cycle of the planet.

__Evidence of Past Climate Change__

Fossil records tell us alot about Earth's climate on time scales of millions of years. The climate has shifted drastically - from almost complete glaciation of the Earth's surface, to pole-to-pole vegetation. In Pennsylvania alone, there have been eras of jungle climate, ice age glaciation, and even an inland sea.

For a more detailed look at climate, scientists have turned to ice cores. These are drill samples taken from deep glaciers or snow caps, which contain trapped air from thousands to hundreds of thousands of years ago. The air is sampled and tested for its composition - carbon dioxide, oxygen, nitrogen, dust, etc. These are good indicators of conditions within the annual snow and ice layers.

The following graph depicts the level of carbon dioxide (red line) and the estimated atmospheric temperature (blue line) over the past 400,000 years from an ice core sample taken in Vostok, Antarctica.

The correlation between carbon dioxide levels and temperature are strong, suggesting that CO2 levels play some role in climate change as a greenhouse gas. However, there is as much as a 6000 year discrepancy (lag) between changes in temperature and changes in CO2 levels, so the amount of CO2 is not always directly associated with climate change.

Here is a look at the past 18,000 years:

And the past 1000 years; note the inlaid graph depicting the past 40 years, as well:



The level of carbon dioxide in the atmosphere is over 100 ppm greater than pre-industrial revolution values, and continues to rise. Because CO2 is a cog in the climate machine, this drastic change (there is more CO2 in the atmosphere now than in any time in recorded history or data) has scientists deeply concerned. How big a factor will CO2 levels play in climate change?





Another cog in the climate change machine is obviously the Sun. Solar output is periodic, meaning it has its lows and its highs, as seen in the following graph: One significant event dealing with solar output was the [|Maunder Minimum], which was a period from 1645 to 1715 when the number of sun spots dropped dramatically (indicating low solar output). This coincided with the [|Little Ice Age], a period in which temperatures in the northern hemisphere were significantly cooler. Whether or not solar output played a role in the Little Ice Age is still debatable, but it may have been a factor.

A longer, more significant cycle is the [|Milankovitch Theory], which takes Earth's movement around the Sun into account for climate variability. There is a 26,000 year precession cycle affecting the Earth's orientation towards the Sun; a 100,000 year orbital shape change; a 41,000 year cycle in axial tilt; and a 70,000 year orbital inclination period. All of these have roles in climate change due to how solar radiation approaches Earth.



Oceans play an important role in climate change, as well. They are able to absorb much more solar radiation than the atmosphere, and will hold that heat longer. They can also store vast quantities of carbon dioxide and are thus considered the largest of Earth's [|carbon sinks]. Ocean currents play vital roles in weather patterns and changes in climate. One of the most famous of these is [|El Nino]. Another example of how oceans affect climate - over the past decade, changes in ocean temperatures and circulation patterns off of New Zealand have created [|extreme drought conditions in Australia].

Ocean temperatures have been on the rise in recent decades:



As water warms, it expands; thus as the oceans warm, they expand, and sea levels rise. Satellite observations have shown a 1.8 millimeter rise in sea levels over the past 50 years. This rise has accelerated in recent years to about 3 millimeters per year, which is a big concern. Thermal expansion is just one factor in sea level rise - melt water from glaciers, the collapse of ice shelves, and deep-water temperatures also affect sea levels.



Rising sea levels threaten coastal cities and low-lying lands, especially those vulnerable to storm surge from hurricanes.

Ocean temperatures are now being constantly monitored by a fleet of robots called [|Argo floats]. These robots are able to provide almost real-time temperature data.