Sometimes it can be unclear how natural and anthropogenic heating of the Earth are different. Throughout Earth’s history, it has gone through phases of frigid temperatures (ice ages) and hot temperatures (interglacial periods). The process responsible for this natural climate change is called the Milankovitch Cycle, named after the Serbian astronomer who calculated the three major factors in the cycle that change the climate. These three factors are:
These three factors all deal with the positioning of the Earth relative to the Sun. The first factor is eccentricity, or the shape of Earth’s orbit around the Sun. Over time, Earth’s orbit will become more or less elliptical on a 100,000-year cycle, changing how close it gets to the Sun as it orbits. You can imagine this by taking a circular orbit and flattening it to make an oval-like orbit. After a while, the now-squashed circle will return to its original form. You can see that, as the shape gets more oval-like, the Earth will get closer and farther away from the Sun as it orbits, much more than when the shape is more circular. Right now, we have a more circular orbit around the Sun.
Next, is the axial tilt of the Earth. This is just as the name implies: the change of tilt of Earth’s axis. Earth’s axis changes from an angle of 21.5 degrees to 24.5 degrees over 41,000 years, which in turn changes how much solar radiation the polar regions receive. The steeper the angle of the Earth’s tilt, the more solar radiation the polar region that faces the Sun receives, and the less solar radiation the opposite polar region receives.
The third and final factor that influences climate in the Milankovitch Cycle is Earth’s “wobble.” This “wobble” refers to where the Earth’s imaginary axis points to arbitrary areas in space. Over about 23,000 years, the axis will complete a circular pattern where it points to different stars in the sky. A common star that is used for reference for this is Polaris, the north star.
This image shows the current phase of “wobbling” of the Earth, compared to the future “wobble” phase of the Earth (Credit: Edward Hahn).
How do these changes in the orientation of the Earth relate to our current problem with climate change? In order to answer this question, we can use the history of Earth’s climate and past CO2 levels in order to understand how we are impacting the natural cycles of change in the global temperature as well as atmospheric CO. Starting at 400,000 years ago, we see from the graph below that Earth’s temperature follows a pattern that oscillates up and down constantly, as do the CO2 levels of Earth. The dips in the graph represent ice ages, while the peaks represent warm interglacial periods.
This graph demonstrates the relationship between CO2 levels and temperature and how they change over time (credit: Environmental Dense Fund).
From the graph, it is evident that CO2 has a strong correlation with the temperature of the Earth, and that CO2 levels are higher than they have ever been in Earth’s recent history. The alarming spike in recent years in CO2 can lead to the conclusion that temperature will also spike like it has in the past. The problem with climate change becomes clear when we closely inspect the cycle’s pattern. The Milankovitch Cycle’s pattern indicates that we should expect to experience falling global temperatures soon, but there is no sign that we will be experiencing any global declines in temperature in the foreseeable future. There is more work to be done in climatological research to discover what impacts humans have had or may have on the planet, and what measures may be taken to avoid potentially dangerous temperature changes.
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© 2018 Weather Forecaster Cole Bristow
DISCUSSION: As planet Earth continues to evolve with time, there is little to no debate that global climate change issues will continue to impact various aspects of the global economy. The greatest concerns are tied to the fact that as the Earth’s average seasonal temperatures continue to gradually increase with time, there will continue to be a proportional increase in the respective energy demands by people from around the world. More specifically, with hotter Summer days, there will be more and more demands for air conditioning resources around the world as well as water demands for both general day-to-day hydration and cool showers. To get a bit more into this issue, there is an exact excerpt attached below from a recent article which was published by the online science writer team from Climate Central which goes into greater detail regarding how this issue has evolved over time.
“Summers are getting hotter and this is coming with a cost. As greenhouse gases build in the atmosphere from the burning of fossil fuels, the number of hotter average and extreme temperatures continues to mount. To better understand how this is impacting local communities, Climate Central analyzed trends in cooling degree days and minimum temperatures for cities across the U.S. in a special report: The High Cost of HOT.
Our study analyzed the number of nights each year when the temperature remained above 65°F (for cities that rarely experience nights above 65°F, we chose 55°F), which is an engineering temperature standard for keeping buildings cool. In our analysis of 244 cities across the U.S., we found that 87 percent are having more of these warm nights since 1970, with the biggest increase in the Southwest. Warming nights are driving the increase in average temperatures. According to NOAA/NCEI, overnight lows since 1900 are warming at a 20 percent higher rate than the daytime highs.
Another way to measure the increase in heat is cooling degree days (CDD), which are used to determine how much cooling is needed to keep a building at a comfortable temperature. CDDs do not actually measure days at all. Rather, they measure the number of degrees that the daily average temperature is above 65°F. So, if the average temperature for a day is 80°F, there were 15 CDDs in that day. Some of the largest increases in CDDs are also seen in the Southwest, however CDDs are increasing sharply in places that traditionally did not need air conditioning in the summer months. For example, the number of CDDs has nearly doubled in San Francisco and Portland, Oregon in the last half-century.”
However, another major issue is the corresponding increase in the cost to power such facilities which are responsible for providing cooling resources. This is a very complicated issue but can nonetheless be addressed through a brief overview of the topic which was reasonably well captured as well by the Climate Central team’s investigations Thus, attached below is another excerpt from the corresponding article which discusses the issues of cost in much greater detail.
“Cooling costs are rising as a result. Air conditioning already makes up the largest share of residential electricity use (17 percent) in the U.S., with Americans spending over $27 billion to cool their homes in 2015. The average annual cost for homes with air conditioning across the U.S. is approximately $250, but in the high use areas of the South, air conditioning costs are almost $450 a year. A 2014 Climate Central analysis of projected future summer temperatures shows that by 2100, New England summers will be as hot as current summers in Florida, dramatically increasing the need for artificial cooling.”
To learn more about the actual warming projections as investigated from across the United States courtesy of the corresponding article generated by Climate Central research team, click here!
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© 2018 Meteorologist Jordan Rabinowitz