Putting Climate Data Into Context

I live in Boulder, Colorado. It’s a beautiful city, and I absolutely love all the nearby mountain activities! Recently, we had a bit of a warm spell. It lasted a while and we were regularly experiencing temperatures in the 50’s (Fahrenheit) which is fairly weird for January. I caught myself feeling some climate change anxiety about this specific bit of warm weather. This is not completely untrue, as humans continue to add more and more carbon dioxide into the air, temperatures will increase on average. However, I caught myself making a fundamental error in my thinking.

The distinction between weather and climate is a very important one. You can never say that the climate is warming just because of one particularly intense warm spell. Instead, you need to look at the overall trend to get any information about the climate. The warm spell I experienced is a case of weather, so we can’t say that is evidence of climate change. However, if the amount of oddly warm days was increasing every year, that would signify a changing climate.

In fact, that is exactly what we see in the image below. Each dot represents the global temperature for each year. It’s been reset so that the average global temperature is 0, and the y-axis shows changes from that average. For example, in the year 2000, air temperature was about 0.4 degrees Celsius warmer than average. There are fluctuations in the data, but the warming trend is clear. Later, I’ll talk about some causes for those fluctuations.

This goes both ways. You can never point to an oddly cold week in the summertime and say that it disproves climate change. In order to study climate, you have to make sure the data is of sufficiently long time. Most climate scientists put the time minimum for climate data at 30 years. Once you have 30 years of data, then you can start making claims about climate. The chart above can be thought of as many snapshots of an evolving climate lined up together since it extends well beyond 30 years.

Any data relating to climate must be put into appropriate context. Much of its information relates to how this data compares to values that have come before. The above example I provided is a classic example of weather vs. climate, but there are many more important distinctions in climate science. In this article, I’m going to share three more important examples of why context matters. We’re going to be covering some very different timescales too, so let’s dive in!

The Oceanic Offset

Climate change deniers will often purposefully remove context from data in order to mislead the public. This is particularly nefarious as it creates a society where most people believe that science isn’t settled yet when over 97% of published papers about human-induced climate change are in agreement. The best way to combat this is through education. Let’s see an example of a common misleading tactic, and why the science says otherwise.

The above image has been presented as evidence to show that the climate is not warming. None of the above data has been fabricated (compare it with the graph above), but it has been presented in a very specific manner. First, notice that only 14 years of data are shown. That is not enough to make any claims about climate, and we know that we have way more data than this. Second, the year 1998 was chosen as a starting point. A very particular climate event happened in that year which creates the perception of a cooling, or at least constant, global temperature.

In the Pacific Ocean, a massive fluctuation occurs called the El-Niño Southern Oscillation, or ENSO for short. This shows up as either a bunch of warming in the Pacific Ocean (called an El Niño) or a significant cooling event (called a La Niña). These events will impact the entire planet and cycle around every 2–7 years. A strong El Niño or La Niña can shift global temperature by as much as 0.3 degrees Celsius! That is a big shift when looking at the y-axis for the above global temperature plots. Because of their importance, climate scientists put a lot of work into predicting them.

The above time series shows the ENSO index over time, note that the y-axis is a special value and is designed to stay flat for consistency and does not show global temperatures. During red periods, an El Niño event occurs, and the planet warms. The opposite occurs during the blue periods. This time series is fairly chaotic but follows a rough cyclic pattern. Notice what’s going on around 1997/1998. The world experienced the largest El Niño event on record! No wonder the plot shows global cooling when it’s zoomed in like that. Several years following have strong La Niña events which would then cool the planet.

In fact, a lot of the wiggles in our global temperature plot make sense with the information. The cool period around 1955 matches a strong La Niña event. There is also a spike in warming during the very large 2015/2016 El Niño.

When looking at global temperature data, make sure you consider the time period being shown. The presenter could be choosing a specific year as a starting point to mislead you. If 1982, 1998, or 2015 is the start, they are probably trying to claim that the planet is not warming. You should also be suspicious if the plot begins in 1973, 1989, or 2000 because they may be trying to make the warming look stronger than what is actually occurring.

Since we have so much temperature data available to us, you should question if a person ever chooses to hide some of it.

This massive oscillation is just one of many climate fluctuations. Wiggles in the data could indicate a variety of different processes are going on. If you have a dataset greater than 30 years, you can safely assume the trend you are observing is being caused by something else external to the climate system. Let’s see another example of an outside force changing our planet’s climate.

The Ice Age Context

We know from a variety of different sources that climate has changed in the past. This goes well beyond our 30-year intervals. Over the past one million years, Earth has cycled in and out of ice ages. This pattern sees the planet warming and cooling by around 5 degrees Celsius, and carbon dioxide in the atmosphere changes by around 90 ppm.

Climate change deniers will often point to this fact as a way to downplay humanity’s role in the current changes that we are seeing. However, this can be very easily disproven. If the theme of this article is a hint, you can probably guess how I’m going to do so. Let’s put the two types of change, natural and caused by humans, that we are seeing into context.

The above plot shows carbon dioxide levels in the atmosphere over the past 800,000 years. This data is the result of an immense amount of work! Most of it comes from ice cores. Scientists drill massive cores down into Greenland and Antarctica to get at the snow that fell hundreds of thousands of years ago. They then extract the air bubbles trapped in it and measure how much carbon is contained in the data. This data is also supported by a vast array of other measurements including fossils, tree rings, and rock information.

Looking at this plot, you can see that yes, carbon dioxide has changed a lot over time. However, the most recent change looks nothing like what has occurred before. It is much faster and goes beyond the range that is expected. What is most striking is that we were already in a period of high carbon dioxide when humans began the Industrial Revolution. That makes recent changes really stick out! Clearly, a different process is at work.

It is generally agreed that these past changes in carbon dioxide are caused by the Milankovitch Cycles. These cycles are super slow and occur on the order of 10,000 to 100,000 years. There is a ton of literature connecting them to the ice ages. My Ph.D. work is devoted to this exact topic. I look at how the Milankovitch Cycles change the oceans in climate models and try to match that up with existing data.

The most important thing to remember here is that Milankovitch Cycles are slow, and humans emitting fossil fuels is fast. The most rapid rise seen in the plot above is still nowhere near as fast as the current changes we are seeing. It is unprecedented in every manner, and this is clearly a change that is not naturally occurring.

A Hot Planet

I want to address one more claim that tries to disprove climate change. Just like the other examples I’ve presented here, it does so by deliberately removing context from the data. About 56 million years ago, we have evidence that the Earth was significantly hotter than it is today by about 7 degrees Celsius. This event is called the Paleocene-Eocene Thermal Maximum, or PETM for short. Climate change deniers love this one because they can point to it and say it undermines all evidence of human-induced climate change. I’ve even had people comment about it in my previous articles.

Again, the timescale matters here. Our best estimates show that it took around 10,000 years to reach this level of warming during the PETM. That is fast, but nowhere near current warming levels. A recent study estimates that if continue down our current path and make no moves toward green energy, we’ll get there in about 150 years. When making comparisons to the past, you always need to consider how quickly the change happened. The faster our planet changes, the more difficult it is for ecosystems to evolve and adapt to it.

These are just some of many examples where context is critical. This is especially true in climate data. Timing is everything!

Going Further

I hope you learned something! Getting climate data into the proper context is essential for understanding it. A public that knows how to question data being presented to them will stay much more informed on important issues. There are plenty of good resources on this topic that I’ve linked below if you want to learn more.

• The Wikipedia page about climate change denial has a lot of interesting discussions. It’s a good starting point to learn more about the strategies employed and how to combat them.
• The IPCC report is a wonderful resource for learning the most recent consensus on climate change. It’s long, but there are summaries available on that website as well.
• The website CarbonBrief has lots of up-to-date news on climate change and what is currently happening in attempts to solve it.
• Bad stories about climate change can be very overwhelming. It’s important to also read articles with good news about the climate such as this one.
• The PETM is a fascinating event in Earth’s history. You can read more about it on this page.

I also have some similar articles to this one that you may be interested in, check them out!

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