The heat wave throughout most of North America in the beginning of April had bought climate change into my mind. Was the heat wave caused by climate change? Likely not, I can’t imagine the effect of climate change happening so abruptly. But it made me think about what really causes climate change on this lovely blue planet of ours?
Weather and Climate
I think the best place to start is to understand the formation of weather patterns and consequently the climate of Earth. Rainy, cloudy, hot, humid, cold, etc. are all considered weather patterns, and the average weather throughout the year(s) is known as climate [1,2]. Ultimately, the sun plays a role in determining the climate as it heats up the earth’s surface as well as the atmosphere–causing various changes in the temperature, pressure, humidity, and so on [1,2].
We know the sun is a very hot object. It can probably melt most of the things here on earth–if not for the various gases in our atmosphere protecting us. Only about 47% of the sun’s energy actually reaches and ends up warming the ground or the sea . Some of the sun’s energy is absorbed by the gases in the atmosphere (~19%), whereas the rest is reflected back into space . Some of the gases that make up our atmosphere trap heat very well, causing the atmosphere to act like a greenhouse. These gases are generally known as greenhouse gases (GHG) .
I’m sure we have all heard of GHG at some point in our lives. It is a hot topic when we talk about climate change. But did you know the number one GHG contributing to the greenhouse effect happens to be water vapor, accounting for 36-70% . The other major contributors are carbon dioxide (CO2) accounting for 9-26%, methane (CH4) accounting for 4-9%, and ozone (O3) accounting for 3-7% . All of these gases are found naturally in our beautiful earth, even before humans massively inhabited the earth. However, the proportions of these gas are affected, such as the amount of CO2, by the industrialization of our civilizations.
There are plenty of books and websites that better discuss the impact of human activities on climate change than I can ever do. So I will focus on some of the natural influences on climate and how they cause complications with determining exactly how large of an effect human activities have on climate change.
Incoming Solar Energy
There are many complicating factors when it comes to climate. For one, the amount of sun’s energy reaching the earth is important since all of the energy we received comes from the sun [1,2]. The sun’s radiance on earth is influenced by several things :
- the wobbling of the earth’s axis which goes a full cycle every 23,000 years;
- the change of the tilt angle of the earth’s axis against the orbital plane which has a period of 41,000 years;
- a change in the shape of the earth’s orbit, which occurs every 100,000 years.
All of these factors change our distance from the sun during the different seasons in the year.
On top of this, the sun’s activity also has periodic fluctuations which go a full cycle every 11 or so years and sees a variation of solar radiance of ~0.1% here on earth [3,4].
Forces of Nature
Aside from human activities, there are some natural events that can also affect the climate on earth. For one, volcanic eruptions can have both positive and negative effects on the temperature here on earth. On one hand, eruptions throw dust and soot into the atmosphere thus blocking some of the sun’s radiation onto the earth’s surface . On the other hand, eruptions also release a large amount of CO2 and methane into the atmosphere hence increasing the GHG concentration and the greenhouse effect .
Similarly, forest fires can also release CO2 into the atmosphere . Although it has been suggested that if a forest of the same size were to grow again, the new trees could remove the same amount of CO2 produced from the fire. Thus forest fires likely affect the GHG concentration only in the short term .
The human contribution to climate change? There are: off gases from various industries, exhaust from combustion engines (i.e. transportation), removal of forests for development and lumber, etc. Enough said.
Pollution in our air also depletes the ozone layer surrounding earth, allowing more UV rays into the atmosphere and onto the earth surfaces which increase the temperature as well .
The Complicated Mess and Controversies
In the past century, the earth’s average temperature has increased by 0.3 – 0.6 oC . Due to the interdependence of these factors, it has been (and still is) very difficult to determine the the actual contribution of any one factor on the climate.
It is quite difficult to obtain an accurate reading of the solar irradiance here on earth for a specific period . There have been large variations in the solar irradiance measured by different studies. One report estimate the 0.1% change in the solar irradiance as a result of solar activities is about 0.24 W/m^2, another estimate it to be 2.5 W/m^2, and yet a third estimate that even 0.24W/m^2 is a gross overestimation .
As Naomi Oreskes mentioned in her essay published in Science , a majority of the scientific literature published with the keyword “global climate change:” between 1993 to 2003 explicitly or implicitly cite the significance of human activities on climate change. Yet, we shouldn’t simply dismiss the findings from studies that conclude differently.
A “minority” of the reports conclude that the various forces of nature is the most significant contributor to climate change. As an example, one study  published earlier this year argues that the climate change that had occurred between 1988 to 2008 is a result of an often ignored change in the tilt of the Earth’s axis.
The tilt of the Earth’s axis is known to vary between 22.1 deg – 24.5 deg in a 41,000 year cycle. Although, newer astronomical models have suggest the range is more likely between 19 – 28.4 deg . The current tilt of the Earth’s axis is believed to average about 23.44 deg. Rivera & Kahn argue in  that the current tilt of the earth’s axis is closer to 27.5 deg. They further suggest that the increased change in the tilt angle is due to the higher frequency of large earthquakes within these past two decades .
The changes to the Earth’s axis means the poles are exposed to more solar radiation. So in fact, the melting ice caps and increases in GHG emissions are also affected by natural phenomenon–not just by human activities as commonly believed.
In the model proposed by Rivera & Kahn, they show that natural forces accounts for 99.9% of the effect of climate change . On the other hand, another study has suggested a more modest value of up to 64%, as reviewed in . These are only two studies out of thousands, and each with models showing different contribution levels of human activities.
In my mind, there’s no doubt both the natural forces and human activities contribute to the climate change. The only remaining question is how much do human activities impact climate change. But only time will tell the damage we may have caused to this planet. In any case, we only have one “blue marble” that we call home–shouldn’t we limit our pollution and take good care of it anyways?
 Wilkinson, J. (2012). The Sun and Earth’s Climate New Eyes on the Sun, (pp. 201-207). Berlin: Springer Berlin Heidelberg.
 Weather and Climate Basics. The National Center Atmospheric Research & The UCAR Office of Program. [Retrieved] May 15, 2012, [from] http://www.eo.ucar.edu/basics/index.html
 Mufti, S., & Shah, G. (2011). Solar-geomagnetic activity influence on Earth’s climate Journal of Atmospheric and Solar-Terrestrial Physics, 73 (13), 1607-1615 DOI: 10.1016/j.jastp.2010.12.012
Lockwood, M. (2011). Solar physics: Shining a light on solar impacts Nature Climate Change, 1 (2), 98-99 DOI: 10.1038/nclimate1096
 Oreskes, N. (2004). BEYOND THE IVORY TOWER: The Scientific Consensus on Climate Change Science, 306 (5702), 1686-1686 DOI: 10.1126/science.1103618
 Rivera, . (2012). Discovery of the Major Mechanism of Global Warming and Climate Change Journal of Basic and Applied Sciences, 8 (1) DOI: 10.6000/1927-5129.2012.08.01.29