Do you currently have the heat on in your house?
Are you wrapped in a blanket as you read this?
Do you own multiple pairs of fuzzy slippers?
If so, you might be wondering: If temperatures are rising, why am I so cold?
First, a little background. When we talk about global warming (one aspect of climate change), we’re referring to a rise in average global temperatures over a period of years – think average trends, not sudden skyrockets. Most scientists are confident that the Industrial Revolution spurred this rise in temperature because, as its name implies, industrialization required huge amounts of fossil fuels, such as oil and coal – which release CO2 into the atmosphere when they’re burned (EPA, 2016).
Below is a quick look at how global CO2 levels have changed over the millennia:
Source: EPA, 2015
It’s pretty clear that global CO2 concentrations made a sharp jump as we became industrialized. For some perspective, check out the graph on the right. It shows a far more gradual increase in CO2 emissions, though it’s hard to overlook the fact that CO2 parts per million (ppm) increased by nearly 100 ppm in just 60 years.
So, do global CO2 levels correspond to temperature? Let’s take a look at the graph below, which shows temperature trends in the continental U.S. only.
Source: EPA, 2016; NOAA, 2016
Notice anything right away? Check out the right side of the graph first: in 2010, the average temperature anomaly (deviation from the norm) reached an all-time high since 1901, at over 3 degrees Fahrenheit. This is happening at every level: record highs for the troposphere (that’s the lowest region of the atmosphere – where we live & breathe) as well as Earth’s surface. (UAH and RSS, the green and yellow lines on the graph, represent different measurement methods employed by the satellite)
You might also notice that there hasn’t been a record low temperature anomaly since approximately 1995. Some of you might be rejoicing at that (no more parkas!), but it’s troubling: average temperatures are rising, and they’re rising more quickly with each passing year.
So what about global temperatures? Warming isn’t just a U.S. problem – we are talking about global warming, after all! The graph below shows temperature trends from a global perspective:
Source: EPA, 2016; NOAA, 2016
It’s pretty clear that the temperature anomaly has hugely increased on a global scale as well – though you’ll notice that the U.S. has a higher-than-average temperature anomaly. Globally, the average temperature chance is only about 1.5 degrees Fahrenheit, which is a tamer number than the U.S.’s staggering 3 degrees. Several factors could explain this, which I’ll talk about in another post.
Like we saw in the first graph, low temperature anomalies are pretty much gone.
What’s bringing the heat?
The scientific consensus around climate change is pretty clear: human activity is contributing significantly to the drastic temperature changes shown in the graphs above. A scientific consensus simply means that the vast majority of scientists – which form a global community and frequently collaborate – agree that something is true based on the available data and evidence. And we have a lot of evidence!
At this point, you might be asking about specific human activities and whether you’re contributing to global warming. We know that burning carbon sources (like oil and coal) releases carbon dioxide (CO2) into the atmosphere, where it then acts as a greenhouse gas to trap the Sun’s heat against Earth’s surface. That heat can circulate, but it can’t dissipate – and so the heat continues to increase, leading to higher temperatures.
I like this inforgraphic from What’s Your Impact?, a neat little website that discusses environmental issues:
What’s Your Impact, 2016
Greenhouse gas emissions have multiple sources. That means driving your car isn’t the only factor contributing to global atmospheric CO2 levels – in fact, our diets may even have more serious an impact on global temperatures than our driving habits! A 2012 publication by UNEP (United Nations Environment Programme) discussed the impacts of meat consumption on greenhouse gases: industrial meat production contributes CH4 (methane, from animals’ gastrointestinal tracts), N2O (nitrous oxide, from nitrogen in feces & urine), and CO2 (carbon dioxide, from deforestation to make way for livestock) to the atmosphere, which make it comparable to transportation and industry in terms of emissions (Scientific American, 2009). With that said, a more recent publication by the EPA shows that agriculture contributed only 9% of greenhouse gas emissions in 2014.
Transportation and industry together contribute to half the United States’ global CO2 emissions. According to a report by the European Commission, more than 70% of transportation emissions come directly from road transport: i.e., the cars, buses, and trucks that we drive everywhere, day in and day out. The EPA has indicated that 61% of all transportation emissions in the U.S. come from light-duty vehicles, like our very own cars. Given that many of our cities and towns are designed to be accessible by car – meaning that they sprawl and cover large distances – it’s not surprising.
Industry is a far more nuanced category, and discussing it would take an entire post by itself! The Guardian does an excellent job of summing these up. I will pull one interesting tidbit from this article, however: deforestation, by itself, generates upwards of 11% of industrial greenhouse gas emissions. Industry itself contributes about 14% of greenhouse gas emissions altogether.
Deforestation!? How can that be? How can tree removal contribute to global warming?
The connection isn’t immediately evident unless you know a little bit about plants. Plants take in CO2 through small openings on the undersides of their leaves. These openings are called stomata and are basically the plant’s respiratory system. CO2 enters the leaf, photosynthesis occurs, and O2 is released as a waste product. When deforestation occurs, fewer plants are available to take in CO2 and release O2. This results in accumulation of CO2 in our atmosphere. Deforestation accounts for 11% of greenhouse gas emissions, but reforestation isn’t keeping up: it only accounts for 0.4% of CO2 emission. So, we are releasing CO2 into the atmosphere far faster than we are removing it.
If you weren’t sure before why you’re still cold despite all the evidence of global warming, hopefully you are now. Average global temperatures are rising. This may not be reflected in every single state at all times – it’s much more evident in coastal areas and regions that are closer to the equator, like many locations along the southern coast of Asia as well as our own west deserts and coast.
Source: EPA, 2015
This is a great graph, but it’s a bit of an eyesore, so let’s break it down. Red triangles indicate the number of days that classify as “unusually hot”, which simply means the temperature is higher than the 95th temperature percentile for that area. So, if a measurement falls within the top 5% of measurements for a specific weather station, it gets a red triangle. Note where those are concentrated: around the coasts and in the deserts. The Midwest, by contrast, has it easier: unusually hot days appear to be decreasing in frequency along the north-south corridor of this region; however, throughout the country, cold days and nights are still becoming less and less common.
Why is this important? For one thing, it shows us that global warming looks different depending on where you are. Accepting this idea is absolutely critical to fully understanding climate change: low temperatures in one area don’t mean low temperatures everywhere. In fact, coastal and desert regions are experiencing the greatest extremes, and if you happen to live in Pennsylvania like me, you’re not necessarily feeling those trends. Although I have only worn my heavy coat a couple of times this winter… Coincidence?