By Ranting Panda, 23 October 2022
In understanding climate change and global warming, it may help to distil the issue down to the most fundamental components:
- Hotter weather causes more severe storms. Warmer oceans tend to create stronger cyclones, hurricanes and typhoons. Heat fuels the intensity of bushfires.
- Carbon dioxide (CO2) is a greenhouse gas (GHG) and affects global temperatures.
Neither of these points is disputed in modern science. It would be surprising to find a climate change denier who would actually dispute either of these points.
The main dispute they have is whether the world is warming and whether humans are the cause of it.
The fact that the world is warming has been quantified in numerous studies, which I'll cover in more detail below.
CO2 emissions have risen dramatically since the mid-20th century and are around 50% higher than they were prior to the Industrial Revolution. Humans are contributing around 36 billion tons per annum of CO2 and other GHG. By comparison, volcanoes contribute around 200 million tons per annum. To make things worse, deforestation is reducing carbon sinks, so less CO2 is absorbed. Agricultural practices release more carbon from the soil, while our heavy reliance on beef has seen a dramatic increase in cattle populations, which produce significant levels of methane, also a GHG. All of these activities are caused by humans and are within our power to control.
Climate deniers have some regular talking points for rejecting the science behind anthropogenic climate change.
They will say that it is part of the common cycles of the Earth, or that back in the day there were hot days, strong cyclones, bush fires etc. They seem to think that scientists aren't aware of previous weather events. However, scientists benchmark and peer review. That's what they do. They actually account for previous weather events and climate changes. Scientists are not stupid, nor are they ignorant. No scientist wants to be known for getting something wrong, so they will test and review their hypotheses ad nauseum before publishing them.
However, there are many who still dispute the very obvious evidence of anthropogenic climate change, so the following points challenge some of the false claims made by climate change denialists.
The world is not warming
The first thing that scientists do is benchmark things. They analysis data to benchmark the current climate and then analyse data to determine how current climate compares to years gone by. These analyses show that the climate is clearly warming. Nineteen of the 20 hottest years on record have occurred since the year 2000 (NASA n.d.[c]).
It is just part of the natural climate cycles of the Earth
We know that CO2 is a greenhouse gas, which means it acts as an insulator to retain heat in the world, somewhat like a doona or a big old blanket. This is not in dispute by any scientist. We know therefore, that increases in CO2 concentration will force the planet to warm.
Milankovitch cycles
Milankovitch cycles are essentially the angle of the earth's rotational axis. Funnily enough, the axis doesn't go straight through the north pole to the south pole. It's a little off-centre. Milankovitch cycles are comprised of three key elements:
- the shape of the Earth's orbit (eccentricity)
- the angle that the Earth's axis is tilted at (obliquity)
- direction Earth's axis of rotation is pointed (precession)
Eccentricity is on a 100,000 year cycle. Obliquity is on a 41,000 year cycle. Precession is on a 25,771 year cycle. On such long cycle times, insignificant changes to Milankovitch cycles over the last century cannot account for the dramatic increase in CO2, global warming or climate change (Buis 2020).
Scientists are making it up
Yeah, but science! Climate is controlled by the laws of physics. Let me illustrate. Most people know that cyclones only form over warm water. Even the most ardent climate denier will agree with that. It is also known, that the warmer the water, the more intense the cyclone will be. Warm water helps create and intensify cyclones.
Ocean temperatures are increasing because of global warming, particularly because of the albedo effect. Albedo measures the ability of a body to absorb or reflect heat. Lighter bodies reflect heat, darker bodies absorb heat. The ocean is a dark body and has a low albedo. In other words, it absorbs almost all solar radiation and heat. Water expands as it heats, which is one of the causes of rising sea levels. As oceans warm, their ability to diffuse CO2 reduces, which means that more CO2 remains in the atmosphere.
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| Ocean heat content (Kaufman n.d.) |
Increased warming is also melting land ice, particularly the Greenland Ice Sheet and the West Antarctic Ice Sheet, both of which are already contributing to increased sea levels. Think this isn't a problem? The Antarctic ice sheet covers 14 million square kilometers and is on average around 2 kilometers thick, although is more than 4.7 km deep at its thickest. It has the ability to raise global sea levels by around 200 meters if it were to all melt.
Heat is also one of the key ingredients in the intensity of fire. The hotter the weather, the more intense the fires will be.
This is all basic and proven science. Scientists are not making this up.
It's all speculation and the 'other side' should also be taught
Ok, so what other side? That heat doesn't intensify storms, cyclones, hurricanes, or typhoons? That heat doesn't intensify fire, warm water or melt ice?
Scientists have quantified increases in CO2 concentrations. This is not in dispute.
Scientists have quantified that the world's climate is warming. This is not in dispute.
The only thing in dispute is whether anthropogenic carbon emissions are driving it. Scientists have run models showing what the climate would be like if there wasn't the increased anthropogenic carbon emissions. These models show that if there had been no change in anthropogenic carbon emissions since the industrial revolution, the world's climate would likely be in a cooling stage now.
What about the Medieval Warm Period?
Again, science! Scientists do actually include such episodes in their research. Guess what? The world is warmer now than the Medieval Warm Period. So what caused the MWP? There was increased solar activity, decreased volcanic activity and changes in ocean circulation that brought much warmer water into the North Atlantic, which caused increased temperatures in Europe. The MWP was largely confined to western Europe and Britain, while other areas of the globe experienced much cooler temperatures.
Although the original hockey stick graph was questioned at the time, there have been a multitude of studies since, which have used numerous other methods for reconstructing historical climate patterns. These reports have confirmed that there is a significant increase in temperatures and atmospheric CO2 levels since the industrial revolution and in particular, since the mid-20th century (Skeptical Science, 2016).
This is all basic and proven science. Scientists are not making this up.
It's all speculation and the 'other side' should also be taught
Ok, so what other side? That heat doesn't intensify storms, cyclones, hurricanes, or typhoons? That heat doesn't intensify fire, warm water or melt ice?
Scientists have quantified increases in CO2 concentrations. This is not in dispute.
Scientists have quantified that the world's climate is warming. This is not in dispute.
The only thing in dispute is whether anthropogenic carbon emissions are driving it. Scientists have run models showing what the climate would be like if there wasn't the increased anthropogenic carbon emissions. These models show that if there had been no change in anthropogenic carbon emissions since the industrial revolution, the world's climate would likely be in a cooling stage now.
Climate change deniers will often state that 3% of scientists dispute anthropogenic climate change. However, studies have found that the conclusions in those papers were faulty and unable to be replicated. Unlike the 97% of papers that found that global warming is real, is problematic and is largely caused by human activity. It should also be pointed out that of that 3%, not all of those scientists actually study climate in any form. This would be tantamount to asking everyone with a trade to comment on the effectiveness of electric vehicles compared to internal combustion vehicles. While some trades would be related, e.g. mechanics, auto-electricians, and even electricians installing EV charging stations, other trades wouldn't have a clue, e.g. butchers, bakers or carpenters. So when unrelated science fields are removed from the survey results and only climate scientists and associated scientists are included, more than 99% believe in anthropogenic climate change and 100% agree that humans are either primary or secondary causes of increasing CO2 emissions.
The sun is warming the planet
The Earth has seen a dramatic increase in warming and greenhouse gases. Yet, there has not been a corresponding change in solar irradiation or warming that would account for the dramatic changes experienced on Earth. The solar energy that Earth has been receiving has followed the natural 11-year cycles of the sun, with no significant changes over the last century that would explain Earth's global warming.
Perhaps the strongest indicator that the cause of Earth's warming is coming from the Earth itself, is that the surface atmosphere has warmed while the upper atmosphere (stratosphere) has been cooling. If the sun was causing global warming, then the stratosphere would also have warmed (NASA n.d.[b]). It is clear that the cause of warming is terrestrial and not solar.
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| Solar irradiation cooling compared to global warming (NASA n.d.[b]) |
What about the Medieval Warm Period?
Again, science! Scientists do actually include such episodes in their research. Guess what? The world is warmer now than the Medieval Warm Period. So what caused the MWP? There was increased solar activity, decreased volcanic activity and changes in ocean circulation that brought much warmer water into the North Atlantic, which caused increased temperatures in Europe. The MWP was largely confined to western Europe and Britain, while other areas of the globe experienced much cooler temperatures.
This differs to today's warming trend, which is global and not simply confined to western Europe or other geographical areas.
The hockey stick graph was fabricated
The infamous hockey stick graph. Perhaps the most controversial graph in modern history.
The graph was a combination of raw instrumental data and proxy data, measuring temperatures from the year 1400 to 1998. The raw instrumental data (e.g. thermometers) was used to record temperatures since 1950. The proxy data was used for data prior to the 20th century. Proxy data is often used in scientific analysis as a substitute for raw measures when scientific instruments are not available. Proxies are generally a good substitute as they provide indications of the phenomena being studied. For example, tree rings are wider during years of higher temperatures and humidity. Ice core samples capture C02, which can indicate higher temperatures. Proxies used by Mann et al in preparing the hockey stick graph included ice core samples, ice melt, ice accumulation, coral growth, tree rings and tree growth trends. They took into account natural climate forcing factors, such as volcanic activity and solar irradiance.
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| Original hockey stick graph showing temperatures from 1400 (Mann et al, 1998, p 783) |
Some have queried the use of proxy data, however an analogy of the use proxies may assist. Dr Chris Cogswell runs a podcast called The Mad Scientist. When discussing proxies used for determining historical climate data, he provided an analogy to simply explain their effectiveness (Cogswell 2017).
The analogy looks at measures of household income. We may have data from some households in which we know specifically how much they earn. This is similar to the modern temperature records where we know exactly what the temperatures have been over the last few decades. However, say we also want to measure wealth in areas where we don't know the actual income. The specific data shows that wealthier households also tend to have larger houses in more upmarket neighbourhoods, they have more holidays and vacation in expensive locations, they own more vehicles which are generally more expensive. These measures are proxy indicators of wealth. Applying those will provide a good estimate of household wealth. However, like any scientific study, the data needs to be calibrated for accuracy. In doing so, it may be determined that the amount of holidays does not necessarily indicate wealth. After all, it may be that executives are under great pressure and expectations, so end up holidaying less, while workers at lower levels in the organisation may have more opportunity to holiday. Of course, location of holiday could still be an indicator of wealth. The hockey stick report by Mann et all (1998) discussed calibration of its data as well.
In 1999, Mann produced a new report measuring temperatures from the year 1000. The revised graph is shown below.
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| Revised hockey stick graph showing temperatures from 1000CE (Mann et al, 1999) |
Although the original hockey stick graph was questioned at the time, there have been a multitude of studies since, which have used numerous other methods for reconstructing historical climate patterns. These reports have confirmed that there is a significant increase in temperatures and atmospheric CO2 levels since the industrial revolution and in particular, since the mid-20th century (Skeptical Science, 2016).
Further studies have considered data over much longer periods than Mann et al did. Current atmospheric CO2 concentrations are the highest they've been in around 1 million years.
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| Atmospheric CO2 levels are the highest they've been in around 1 million years (NASA n.d.[a]) |
Conclusion
Global warming is happening and it is forcing climate change. It is imperative that we reduce our carbon emissions to net zero as quickly as possible. The big concern is that we reach a tipping point, in which the world will continue warming under the weight of the increased atmospheric CO2 reservoir which will drive greater feedback, that is responses to warming, which in turn contribute to climate forcing factors that continue increasing GHG and forcing up temperatures. The tipping point is a point of no return, because at that point, our ability to reduce atmospheric CO2 concentrations will be outside our control and the world will continue warming uncontrollably. Sea levels will continue to rise, species will become extinct (as we are already starting to see), some plants will be unable to grow. All of this will affect our ability to continue an existence as we know it.
Sources and references
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