Who done it?
Understanding the factors behind the recent change in global climate is not only an important scientific question, but given the impacts that warming has on our planet as a whole, it is an important piece of information needed to better prepare society and the environment for what might lie ahead.
We do not know everything about climate science, much like other scientific disciplines; however, we can come up with several factors that may be associated with the changes observed to date.
Suspect #1: The sun
Suspect #2: Volcanic activity
Suspect #3: Orbital cycles
Suspect #4: Greenhouse gases
Suspect #5: Natural climate variability
There may be other suspects that scientists have yet to identify as being players in observed changes to date. However, significant research has not identified any additional processes thus far.
We do not know everything about climate science, much like other scientific disciplines; however, we can come up with several factors that may be associated with the changes observed to date.
Suspect #1: The sun
Suspect #2: Volcanic activity
Suspect #3: Orbital cycles
Suspect #4: Greenhouse gases
Suspect #5: Natural climate variability
There may be other suspects that scientists have yet to identify as being players in observed changes to date. However, significant research has not identified any additional processes thus far.
Suspect #1: The sun
While an increase in solar activity was observed from the mid 1800s through the mid-1900s, significant warming since 1970 coincides with a flattening and potential minor decrease in solar output. The overall increase in solar activity during the early 20th century equates to an extra 0.1 Watts per meter square at the Earth's surface. The divergence of solar activity and temperature suggests that the sun has not been a factor in most of the observed warming since 1950 but may have contributed to early 20th century warming.
Suspect #2: Volcanic Activity
There is little evidence to suggest that vulcanism is behind the warming trend observed for the past 150 years. A reconstruction of volcanic aerosols shows that while the late 19th century featured significant volcanic activity, the latter half of the 20th century did likewise. Volcanic eruptions do emit carbon dioxide to the atmosphere. However, the magnitude is approximately 100 times less than the amount of carbon dioxide human activities have put into the atmosphere averaged over the 20th century.
Suspect #3: Orbital Cycles
Orbital cycles operate over tens of thousand of year timescales. The key to warming processes due to orbital factors is to increase the amount of sunshine at 65-degrees North latitude during the summer months that can force the melting of ice sheets. A time series of solar radiation averaged across all longitudinal bands for June 30th is shown to the left. The x-axis shows time, from 25,000 years ago to 25,000 years from today. The peak radiation at 65-N occurred 10,000 years ago when we were closer to the sun during Northern Hemisphere summer. Indeed when looking at long term temperature reconstructions, global temperatures have cooled for the past 8,000 years by a couple tenths of a degree Celsius per millennia.
Go back and review Orbital Variations and their influence on climate by logging in to BBLearn and go to Module 8. Click on the Study Area icon, and in the Study Area, under Interactive Animations for Chapter 8, select 'Orbital Variations and Climate Change.'
Go back and review Orbital Variations and their influence on climate by logging in to BBLearn and go to Module 8. Click on the Study Area icon, and in the Study Area, under Interactive Animations for Chapter 8, select 'Orbital Variations and Climate Change.'
Suspect #4: Greenhouse Gases
Since 1850 we have seen approximately a 30% increase in atmospheric carbon dioxide and methane concentrations. Although there are natural sources of these greenhouse gases, isotopic studies suggest the changes are associated with mankind. Moreover, the levels of carbon dioxide and methane in our atmosphere today have not been observed for 3 million years and are clearly outside the range of the natural fluctuations between glacial and interglacial periods. While past temperature and CO2 have tracked one another over glacial periods and over geologic changes in climate, does that convict carbon dioxide and other greenhouse gases of the current warming? Not necessarily, but it is a leading candidate as it logically results in more heat trapping of the atmosphere. Estimates are that an additional 2.8 Watts per meter square have been trapped due to these increases in greenhouse gases since 1850.
Suspect #5: Natural Climate Variability
Natural climate variability including El Nino have important impacts on climate on a year-to-year basis. Years with El Ninos typically are warmer globally than years with La Ninas. A strong La Nina that developed in 2008 resulted in January 2008 global mean temperature 0.8C cooler than January 2007. Some reported that "one year of cooling wiped out a century worth of warming". However, such views are typically short sited as El Nino events are short in the grand scheme of things. However, at time scales of 10-20 years, changes in the distribution of El Nino vs. La Nina events can influence short-term climate trends. Noteworthy in the recent discussion of temperature trends since 1998 is the dominance of La Nina events. However, if we examine global temperature records by El Nino years (red), La Nina years (blue), and La Nada or neutral years (gray), we find that generally, El Nino years have been getting warmer, La Nina years have been getting warmer and Neutral years have been getting warmer. Over the past century, there has not been any long term change in the frequency of El Nino events however, suggesting that natural variability is not a prime suspect.
Log onto bblearn and go to Module 8, click on Mastering Assignments and complete "Assignment 8.2: Atmospheric CO2 and Temperature Changes"
Log onto bblearn and go to Module 8, click on Mastering Assignments and complete "Assignment 8.2: Atmospheric CO2 and Temperature Changes"