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The Hockey Stick · The Climate Translation

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  It's one of the most iconic and probably most hated images in the history of climate
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  science.
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  To some, it's a smoking gun for human-driven global warming.
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  To others, it's statistical nonsense.
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  But what exactly is the hockey stick graph?
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  And why has it spent nearly 30 years in the crosshairs of the climate wars?
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  Welcome to the podcast, I'm Dr. Mack, and this is the Climate Translation.
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  If you close your eyes and imagine a standard hockey stick, you're already looking at one
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  of the most important data sets in human history.
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  The graph was first published in a landmark 1999 paper by Michael Mann and his colleagues.
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  It was designed to show how the temperature of the northern hemisphere has fluctuated
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  over the last thousand years.
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  But why a hockey stick?
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  Let's break it down into the two parts of the tool.
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  Imagine a long wooden handle stretching horizontally across your field of vision.
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  This represents the year's 1,000 to about 1,800.
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  In the graph, the line is relatively flat.
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  It has some slight wobbles, showing some gradual warming and cooling trends over nine centuries.
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  It represents a world before the industrial revolution, where the climate shifted slowly
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  due to natural forces.
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  Now imagine the very end of that long handle.
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  There's a sharp, near vertical curve pointing straight up.
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  This is the blade of the stick, and it represents the 20th and 21st centuries.
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  This is where the data shows a temperature spike so rapid and so steep that it looks like
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  a total departure from the previous thousand years.
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  When scientists look at this, the blade is the flashing red light.
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  It tells us that what we are experiencing right now isn't just natural wobble like in
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  the handle.
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  It's a historic break in the pattern.
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  Now for the everyday person, the question is often, why does this one graph cause so much
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  fighting?
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  It's because it simplifies a very complex story into one inescapable image.
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  If the hockey stick is right, then our current warming isn't business as usual for the planet.
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  It's a massive human driven acceleration.
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  This is why the graph has become a focal point in the climate wars.
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  Misinformers have spent decades trying to break the stick because if you can convince people
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  the graph is wrong, you can convince them the current warming is just another natural
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  cycle.
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  But as we're going to see, it's not just one graph anymore.
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  Since 1999, the science has only gotten more precise, adding more layers to that handle
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  and making the blade even sharper.
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  Now whenever I show the hockey stick in my classroom, I have at least one student that inevitably
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  raises their hand and asks the million dollar question.
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  Dr. Mack, how can you possibly know what the temperature was in the year 1200?
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  We didn't even have the monitors, satellites, or weather aspects then.
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  It's a great point!
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  Reliable direct temperature measurements only go back to about 1850 in the UK and 1880
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  in the US.
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  To see further back, hundreds or even thousands of years, we have to look at the natural
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  tape recorders of Earth's history.
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  In science, we call those proxies.
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  A proxy is simply something in nature that records a signature of the weather at the time
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  it was formed.
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  In a crime scene, where a detective finds a footprint.
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  The detective didn't see the person walk by, but the footprint acts as the proxy for
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  their shoe size and their weight.
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  We do the same thing for climate.
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  One proxy we can use is tree rings.
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  Certain very old trees have lived through the centuries.
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  Just like a gardener knows that some years are better for growth than others, trees record
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  this in their wood.
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  Think of a tree ring like a social media status update for that year.
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  In the good year, one that's warm and has plenty of rain, the tree is happy.
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  It grows a lot, and it creates a wide light-colored ring.
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  In a bad year, maybe a cooler season or one with a massive drought, the tree struggles
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  and grows a very thin, dark, dense ring.
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  By counting back from the bark of today to the center, which represents the past, we
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  can read those status updates to see exactly which years were toaster and which were cooler.
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  If tree rings are a diary, ice cores are Earth's security camera footage.
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  We go to places like Greenland and Antarctica and drill miles down into the ice.
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  Think of an ice core like a layered parfait that's been sitting in the freezer for thousands
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  of years.
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  Every year, snow falls and gets squashed down into a new layer of ice.
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  Trapped inside that ice are tiny microscopic bubbles of air.
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  When we pull that core up, those bubbles are literal time capsules.
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  We can pop them in the lab and breathe in the air from hundreds even thousands of years
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  ago.
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  We can directly measure how much carbon dioxide was in the air and use the chemistry of the
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  water to calculate the temperature of the snow when it fell.
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  But there are other records as well.
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  Down at the bottom of our oceans and lakes, there's a constant snow of dust and dirt and
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  tiny shells of microscopic creatures.
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  Think of these sediments like the junk drawer of the planet.
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  Something that happens in the water eventually settles at the bottom.
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  There are tiny organisms called foraminifera that grow shells.
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  The chemistry of those shells changes depending on how warm the water was when they were alive.
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  When they die, they sink and become part of the mud at the bottom.
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  We take cores of that mud, almost like we're using a giant straw to pull out a vertical
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  slice of the seafloor.
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  By looking at which creatures live there and the chemical makeup of their shells, we
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  can determine the ocean temperature from centuries ago.
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  Now critics often say, but the tree rings aren't perfect, they have uncertainty.
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  And they're right.
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  Proxy data does contain more uncertainty than modern digital thermometers, which are
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  very precise.
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  Everyone in science knows that.
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  But here's the secret.
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  You don't just use one tree or one ice core.
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  You cross check.
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  If the tree rings in North America, the ice bubbles in Antarctica and the sediment cores
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  off the coast of Europe all show the same cooling trend and let's say the year 1200, confidence
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  goes way up.
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  It's like having ten witnesses to a car accident.
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  Even if one person's memory is a little fuzzy, when they all describe the same red car,
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  you can be pretty sure there was a red car.
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  By 1999, our confidence in these proxies was strong enough to link them to our modern
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  thermometer readings.
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  The result was the iconic hockey stick shape, a long, slow, slightly wobbling handle
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  followed by a modern blade sticking straight up.
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  Now, we get into the climate wars, because the hockey stick was such a powerful, easy
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  to understand image, it became a massive target.
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  If you were someone who didn't want to believe in human cause warming, the blade of that
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  stick was your biggest enemy.
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  In 2003, two researchers, Macintyre and McKittrick, published a critique claiming the hockey
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  stick was statistical nonsense.
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  They argued that the math used to create the graph was so flawed that you could feed
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  it random noise and it would still produce the same shape.
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  You might still see that today in social media comments or on certain news segments,
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  the claim that the hockey stick is broken or has been debunked.
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  So as an educator, how do I explain this to a student that has seen those headlines?
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  Well, I use a security camera analogy.
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  Imagine a security camera catches a thief in a store.
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  The footage is a bit grainy and the defense attorney argues in court that the camera
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  lens was distorted.
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  They claimed the footage is broken and shouldn't be used as evidence.
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  In a courtroom, that might work if there was only one camera, but wouldn't there are
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  more cameras and they all show the same thing.
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  In science, we don't stop at one camera.
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  Since that first paper in 1999, the science has moved on, independent teams of scientists,
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  people who had nothing to do with the original study decided to check the math.
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  They used different statistical techniques and gathered even more data from different
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  proxies like corals and stalagmites which have rings like trees and sediment bore holes.
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  And here's the light bulb moment, they all found the same result.
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  They did a deep dive and confirmed that while the math from the original 15th century data
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  had some minor uncertainties, the overall blade portion, the unprecedented warming
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  of the past few decades was absolutely real.
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  Using sediment cores, scientists looked at temperatures deep underground in North America
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  and Europe and in Africa.
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  Even without tree rings, they found the 20th century was the warmest in 500 years.
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  Records from the cross sections of stalagmites and underground caverns confirmed that the
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  20th century temperatures exceeded anything in the last half millennium.
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  The broken stick argument is what we call a manufactured controversy.
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  It fixates on one 27-year-old paper while ignoring the mountain of evidence that has been
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  built since then.
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  Today, we have even more striking visuals, like Ed Hawkins warming stripes.
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  It essentially is the hockey stick for the 21st century.
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  Using 20 years of additional scientific progress to show a clear, undeniable transition from
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  the cool blue centuries to the burning red decades of the recent past.
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  So is the stick broken?
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  No.
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  It's been poked, prodded, and put under a microscope by every skeptic on the planet.
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  And after all that, as Elton John says, it's still standing.
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  Now for the final piece of the puzzle, I often hear people say, so what if the graph has
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  a blade?
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  The handle has wobbles too.
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  The climate has always changed.
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  As we've discussed in previous episodes, they're right, it has.
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  But to understand why scientists are so concerned about the hockey stick, we have to talk about
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  acceleration.
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  I want you to imagine you're a passenger in a car on a cross-country drive along a long
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  highway, let's say in the Great Plains.
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  For the first 900 miles of the trip, the car is on cruise control, doing a steady 45
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  miles per hour through the mostly flat terrain.
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  That's the handle of our hockey stick.
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  At that speed, you can relax.
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  You can sip on your coffee, look at the scenery, read a book, or even maybe listen to this
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  podcast on your radio.
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  If the car hits a small bump or the speed drifts up to 48 or down to 42, you barely notice.
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  The system is stable.
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  But suddenly you look at the driver, and their eyes are fixed on the horizon.
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  They slam their foot on the accelerator all the way to the floor.
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  In a matter of seconds, the car screams from 45 miles an hour to 125.
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  Now think about what happens inside that car.
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  Your coffee spills everywhere.
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  Your back is slammed into the seat.
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  The engine starts to whine under the stress, and the tires are struggling to grip the pavement
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  because they weren't designed for that kind of friction.
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  Welcome to the blade.
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  The problem isn't that the car is moving, it's the rate of change.
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  Our entire civilization, our coastal cities, our massive wheat fields, our water systems,
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  they were all built during that 45 mile per hour cruise control of the last thousand years.
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  We simply are not designed for the 125 mile per hour acceleration we're seeing in the
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  geologic record right now.
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  When we look at the hockey stick, we aren't looking at warming, or looking at a system
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  that has lost its balance.
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  We're seeing changes that normally take a million years, occur in just 200.
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  Now for those of you that know the graph, you probably can relate.
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  You mention the hockey stick and your skeptical cousin or your neighbor brings up a blog
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  post they read about broken math or dishonest scientists.
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  Your instinct might be to go to data, and while that's great for a scientist, there
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  are better ways to bridge the gap.
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  When someone says the data is unreliable because we didn't have thermometers in the year 1200,
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  ask them if you wanted to know what happened at a house fire, would you only talk to the
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  one person that had a camera, or would you go to the neighborhood smell smoke, the person
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  who saw the glow from a mile away, and the gardener who found ash on the leaves.
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  Explain that proxies are those witnesses.
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  We aren't just looking at one tree ring sample.
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  We're looking at ice cores, stalagmites, corals, lake an ocean sediments.
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  When the witnesses from all around the world all tell the same story, a long stable handle
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  and a sudden, sharp blade, that's not a fluke, that's a consensus.
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  If they bring up the 2003 debunking of the original graph, use a map analogy.
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  The first maps of North and South America were crude.
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  Back then, the first explorers used the tools they had, sextants and the stars, to draw
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  the coastline of a new continent.
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  It wasn't perfect.
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  Maybe they missed a few emlets, or the shape of the bay was slightly off, but they clearly
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  show that massive continents existed.
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  The first version of the hockey stick graph in 1999 was like the first hand drawn map
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  of the new coastline.
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  It had some wobbly lines, but it proved something was there.
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  Today we have the equivalent of a 4K satellite GPS image that makes the graph even sharper.
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  The goal of these conversations isn't to make your friend a climate scientist.
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  It's to help them realize that the controversy is often a distraction, from a very simple,
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  very visible reality.
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  The rate of change we're seeing right now is unlike anything humans have ever dealt
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  with.
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  We can't explain it in a way, and we ignore it at our peril.
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  We've covered a lot of ground in these first three episodes.
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  We've looked at the rate of change, we've deconstructed the consensus gap, and today we
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  looked at the hockey stick, the graph that perfectly illustrates the world we're moving
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  into.
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  I hope these translations help you to see the atmosphere a little more clearly.
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  More importantly, I hope they help you build a bridge to someone else, because we can't
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  fix a world we don't understand, and we can't understand it if we're shouting at each
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  other.
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  I'm Dr. Mack, and this has been the Climate Translation.
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  If you have a question about the climate that you've been too afraid to ask, or if you
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  have differing opinions, please let me know.
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  I can use your viewpoints in future episodes.
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  You can reach me at the climate translation at gmail.com.
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  I'll see you next time.