Climate Change: Could it just be natural? Part 2

By Beatrice Omotosho

Climate as a Phenomenon

 Climate is characterized by mean air temperature, humidity, winds, precipitation, and frequency of extreme weather events over a lengthy period of time, at least thirty years scientists say. The climate forms and follows long term trends usually of periods of warming and cooling. Climate change is therefore a natural phenomenon, but of course who didn’t know that? However, this is only the case when it occurs steadily, over a significantly long period of time, such as 100,000 years or more not 60/70 years like we are seeing today. Earth’s atmosphere is chaotic; a little like me before a 9am lecture, and this is why we see such high variability in weather patterns, not because of me, we’re back to the climate now. However, unlike weather, climate is a lot more stable and change occurs over many decades. This change is measured by climatologists across the globe using different methods and data such as weather station records, situ thermometers, remote sensing, tree rings, Antarctic ice deposits, instrument records from land stations and ships etc, how they extract information from ice, beats me. These observations have shown that earth’s climate has changed significantly since 1900 (I mean it would be strange if it didn’t), largely due to increased concentrations of Greenhouse gases (GHG) in our atmosphere.

The main GHG’s are, N2O, CH₄, CO2 and H2O, and their increase means earth has seen a gradual warming over the last 100 years, particularly since the early 1980s, due to the intensification of the greenhouse effect illustrated in figure 1. Figure 1 shows this in terms of energy flows, illustrating the necessary balance between short wave and long wave radiation specifically for years 2000-2004. It shows the flow of energy in proportion to their actual importance through the use of black arrows. These energy flows are not always balanced (like my diet) creating energy surpluses in tropical regions and deficits in polar regions, hence energy is transferred poleward to maintain a balance, this is illustrated by Figure 2.

The Data

Since 1880, global land and ocean yearly temperature has increased at an average rate of 0.07°C per decade, and since 1980, this rate has been twice as high. From figure 3, we see that from 1980, earth’s global surface temperature really started to increase and even more rapidly, since the late 1990’s, with the warmest 10 years recorded since 1998, 9 of which were after 2005. We see this upward trend in global mean temperatures in figure 4.

Natural Influences on Global Climate: Orbital and Solar Variability

The key natural influences on Global Climate are orbital variations, solar variability, volcanic eruptions, El Niño events and naturally occurring GHG. Orbital variations influence the climate, as they govern the timing of glacial and interglacial periods. This however takes place over thousands of years and therefore you can tell those ‘natural climate change’ believers, that this definitely doesn’t play a role in climate change since 1900s. Solar variability refers to changes in the radiation that the sun emits such as the variation with the 11-year oscillations of the sun’s energy output known as the sunspot cycle and also other long- term variations i.e. “geopotential height variations”.

The main causes of solar variability are solar evolution which is fuelled by the conditions in the Sun’s core, and the sun’s magnetic field. These 11-year oscillations are often illustrated by sunspots (a cool region associated with convection, shown in Image 1), which is how solar activity and energy output was previously recorded for a long time, before satellites enabled direct observations. When plotted on a graph, (Figure 5), we see the total solar irradiance since 1978 and an amplitude of about 0.1 per cent. When plotted against a graph of climate records of average temperatures (Figure 6), we notice there is actually no close correlation between the two since 1900s. A steep rise in temperature post 1980s, leaves irradiance far behind, subsequently meaning that unlike orbital variations, though more relevant, but likewise, it still cannot explain the recent rise in temperatures that has been observed since the 1900s, at best, there is a “weak secular trend”. So out goes another argument for those saying this is all natural. In part 3, I will explore volcanic eruptions, El niño events and other natural issues.

Figure 1: Global annual mean earth energy budget for March 2000 to may 2004 period
Source: Trenberth et al, 2008
Figure 2: energy
Source: (secondary) Doug Benn, 2019
Figure 3: History of Global surface temperature since 1880
Source: NOAA, 2019
Figure 4: Global mean estimates
Source: NASA, 2019
Image 1: Sunspot and surrounding photosphere
Source: Solanki, 2002
Figure 5: solar irradiance
Source: Solanki, 2002
Figure 6: temperature anomalies
Source: Solanki, 2002

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