I. The oceans are warming:
If the Earth is warming the majority of the excess heat is expected to go towards warming the oceans. Because the oceans have a very large heat capacity (1,000 times that of the land and the atmosphere) their overall temperature is not easily affected. Hence, any short-term weather pattern wouldn’t affect their temperature. So, if the oceans have been continuously warming over a period of about 50 years we can conclude that the earth is experiencing a long-term warming trend.
All the data collected since 1955 shows that the oceans are warming quickly, with a great amount of increase just recently. Lyman et al. (2006) report a measured increase in the heat content of the upper 750 m of the world oceans by 8.1 (± 1.4) x 10^22 J between 1993 to 2003, followed by a decrease of 3.2 (± 1.1) x 10^22 J between 2003 and 2005. Willis et al. (2007) corrected this with the finding that the cooling was an artifact attributed to instrument bias. Incorporating this correction to their data they found the oceans experienced a warming between 1993 and 2005 that required an average rate of warming of 0.33 ± 0.23 W/m2 over the Earth’s total surface area. An important note is that while the cooling was attributable to an artifact, the measured heating of the ocean reported by Lyman et al. between 1993 and 2003 was real. [1]
Levitus et al. (2008) compared several independent studies of the ocean's temperatures. All the studies agreed that the ocean’s temperatures were rising. [1]
II. The atmosphere is warming:
The greenhouse effect occurs because greenhouse gases let sunlight (shortwave radiation) pass through the atmosphere. The earth absorbs sunlight, warms, then reradiates heat (infrared or longwave radiation). The outgoing longwave radiation is absorbed by greenhouse gases in the atmosphere. This heats the atmosphere which in turn reradiates longwave radiation in all directions. Some of it makes its way back to the surface of the earth. So with more carbon dioxide in the atmosphere, we expect to see less longwave radiation escaping to space at the wavelengths that carbon dioxide absorb. We also expect to see more infrared radiation returning back to Earth at these same wavelengths.
A recent study analyzed data collected by NASA's Nimbus 4 spacecraft, which surveyed the planet with an Infrared Interferometric Spectrometer (IRIS) between April 1970 and January 1971, and the Japanese ADEO satellite, which utilized the Interferometric Monitor of Greenhouse Gases (IMG) instrument, starting in 1996. To ensure that the data were reliable and comparable, the team looked only at readings from the same three-month period of the year (April to June) and adjusted them to eliminate the effects of cloud cover. Researchers looked at the infrared spectrum of long-wave radiation from a region over the Pacific Ocean, as well as from the entire globe. The findings indicated long-term changes in atmospheric CH4, CO2, ozone (O3) and CFC 11 and 12 concentrations and, consequently, a significant increase in the earth's greenhouse effect.
Another study found an increasing trend of more longwave radiation returning to earth, attributed to increases in air temperature, humidity and atmospheric carbon dioxide (Wang 2009). More regional studies such as an examination of downward longwave radiation over the central Alps find that downward longwave radiation is increasing due to an enhanced greenhouse effect.
2009 was tied for the second warmest year in the modern record, a new NASA analysis of global surface temperature shows. The analysis, conducted by the Goddard Institute for Space Studies (GISS) in New York City, also shows that in the Southern Hemisphere, 2009 was the warmest year since modern records began in 1880. [2]
III. Weather isn't climate:
Many deniers argue that global warming can't exist because of the cold temperatures. What they don't understand is that weather isn't climate. The weather in an area is always changing. However, the climate of a region generally remains the same.
Due to the atmosphere's low heat capacity, its easily effected by short-term weather patterns, unrelated to global warming. Even though the ocean has a higher heat capacity, it too is sometimes effected by short-term weather patterns.
For example, many deniers believed that global warming stopped in 2008.Climatologists at the NASA Goddard Institute for Space Studies, in New York City, found that 2008 was the coolest year since 2000. However, most of the world was either near normal or warmer in 2008 than the norm. Eurasia, the Arctic, and the Antarctic Peninsula were exceptionally warm, while much of the Pacific Ocean was cooler than the long-term average. [3]
The relatively low temperature in the tropical Pacific was due to a strong La Niña that existed in the first half of the year, the research team noted. La Niña and El Niño are opposite phases of a natural oscillation of equatorial Pacific Ocean temperatures over several years. La Niña is the cool phase. The warmer El Niño phase typically follows within a year or two of La Niña. [3] However, temperatures would rise again in 2009, even though 2009 wasn’t a El Niño year. This shows that the recorded cooling (in 2008) was only a short-tern weather effect.
"There's always an interest in the annual temperature numbers and on a given year's ranking, but usually that misses the point," said James Hansen, the director of GISS. "There's substantial year-to-year variability of global temperature caused by the tropical El Niño-La Niña cycle. But when we average temperature over five or ten years to minimize that variability, we find that global warming is continuing unabated." [2]
IV. Global warming isn't caused by Earth's internal heating:
Many deniers of AGW argue that global warming is caused by Earth's internal heating, which is caused by radioactive decay of unstable isotopes. We can assume that these isotopes are not uniformly distributed within the Earth’s interior and that they move around as internal convection occurs.
Deniers argue that there is a possibility that isolated concentrations of radioactive isotopes are brought together by this convective motion and this would lead to increased levels of radioactive decay.
However, upon further examination this is clearly not the case. The global warming effects we are witnessing have been widespread and have been occurring on a short time scale, even by human standards. This does not lend itself to the idea of a large amount of convective activity bringing isolated concentrations together within the Earth’s interior, an activity that would require a timescale of hundreds of thousands to millions of years.
Even if this activity had occurred in the past such that the effects were now being witnessed, this effect would not be something that manifests itself suddenly or uniformly. Infrared measurements of the Earth’s surface have not revealed widespread areas of unusual heating. There are isolated hotspots, but they are limited in scope, both in spatial dimensions and in temperature variations. Spots such as these do not produce enough heating to have resulted in the temperature increases, or to even produce anything other than an extremely small fraction of this observed heating. [1]
V. Global warming isn't caused by solar irradiance:
Measurements show that solar irradiance has decreased over this period. [4]
VIII. Man-made emissions, not natural emissions, are causing GW:
Studies have shown that approximately 45% of all anthropogenic emissions are absorbed every year [Barker and Ross (1999)]. Every year, humans release 30 billion tons of CO2.This would increase the amount of CO2 in the atmosphere by approximately 165 billion tons between 1993 and 2003. This would mean that during a ten-year period, manmade emissions have increased the amount of CO2 in the atmosphere by an amount equal to the total amount of gases emitted by all volcanic sources over a period of more than 650 years. [1]