Scientific consensus is not an easy thing to come by. If you’ve ever known a scientist you’ll know that they demand evidence for everything. Even then, some evidence is not enough. How was the data collected? Was the experiment randomized or blinded? Was the study published in a reputable peer-reviewed scientific journal? Even then, one study could be an anomaly. Have the results been reproduced? Are there other studies that support the conclusion? Are there any systematic reviews, studies of all the studies, supporting the conclusion? Are there multiple independent lines of evidence that support the theory? Then, and only then, will the scientific community accept the results as fact. This is why when a scientist in-the-know hears that any issue has achieved 99% consensus, their jaw may hit the floor.
Such is the case with human caused global climate change. The first scientific publication predicting global warming caused by the burning of fossil fuels was published in 1824. Still, it wasn’t until the 1950s that numerous scientists from many different fields came to the same conclusion. Better technology, more data, more publications, and greater and greater consensus grew in tandem with the rise of the environmental movement of the 1980’s. Even then, another 20 years passed before the scientific community agreed nearly unanimously: climate change is real and is caused by human activity. So what are the some of the most compelling lines of evidence? Below is a list of my top five:
- CO2 and global temps.- Perhaps the most famous data of all, thanks in large part to Al Gore’s “An Inconvenient Truth”, is the correlation between rising levels of atmospheric carbon dioxide and average global temperatures. Graphs displaying this correlation are striking, but alone they fall short. Most folks, even non-scientists, know not to conflate correlation with causation. Obviously scientists have thoroughly flushed this one out, proving beyond a reasonable doubt that it is in fact carbon dioxide absorbs radiated heat and that the levels of carbon dioxide in our atmosphere today are due to human emissions. Remember, that in the summary above, which takes up just a few lines, there are literally decades worth of research and scientific bickering.
- A warming ocean- To many scientists the correlation between atmospheric greenhouse gases and the temperature of our oceans is the most compelling. That is because climate scientists understand, just as you do if you read last week’s blog, that it is not easy to change the temperature of the oceans. Enormous amounts of thermal energy are required to heat up these vast bodies of water by even a fraction of a degree. Hot days yield cool nights and summer eventually turns to winter, so atmospheric temperatures can be deceiving (though the trend is clear there as well), but not the oceans. Ocean temperatures have been steadily rising at a rate that tracks perfectly with measures of atmospheric greenhouse gases.
- Mega hurricanes- for decades oceanographers and climate scientists have understood how warm ocean water creates the conditions to create hurricanes. That was a pretty easy conclusion given that hurricanes only occur during hot summer months and in our warmest patches of ocean. If we can accept that our oceans are warming then the prediction the number and intensity of hurricanes should be on the rise is pretty much a no-brainer. You don’t need to measure greenhouse gas emissions in this case.
- Coral bleaching- Perhaps you’re not any type of climate scientists, preferring instead to spend your days collecting data while diving on a coral reef (gee, tough gig). Marine biologists have witnessed enough coral bleaching events in the past to figure out the correlation between that and a warm influx of water, perhaps from an El nino event. Replicated in wet labs a hundred times over, marine biologists replicated the effect. So then, if the oceans are warming shouldn’t we expect to see an increase in the number and severity of coral bleaching events. You guessed it! The number of coral bleaching events has risen dramatically in the past few years, leading many to predict a catastrophic collapse in the world’s coral reefs within the next decade.
- Sea level rise- Water expands as it is heated. Crazy, right? I mean, I’ve never heated a pot of water to below boiling and had it overflow. The effect is real but it is very small, therefore undetectable in your puny cooking pot. However, given enough water and the effect is undeniable. Ignoring the addition of melting glacial ice, a warmer should expand causing seal level to rise. The numbers don’t lie and neither does NASA.
By and large the tedious process of scientific discovery remains out of sight and out of mind of the public’s conscience. People want a quick clean answer, rather than scientific bickering and incremental steps. Unfortunately, good science is painstakingly tedious and tremendously complex. So the next time you hear someone cast doubt on climate change, give ‘em a little pep talk on just how hard it was to come to the current consensus. You can tell them I sent you.