Friday, March 4, 2016

Curiosity Challenge: "What is Global Warming?"

“What is Global Warming?”  -- Madi Corvi, Age 12

You’ve asked a very important question, Madi, and one of my favorite topics to talk about!  Lots of scientists have been wondering what has been causing the hottest years on record (most of which have been happening in the past decade), and if humans are part of the cause.  They agree that the earth has been heating up and cooling because of natural reasons (like volcanic eruptions, or changes on the sun) for thousands of years...but the recent temperature increase has been sharper than ever before.  Since that temperature spike has occurred during the time when humans have been on the planet, most scientists agree that humans are probably the cause.  When talking about global warming, it’s important to make it clear whether we’re talking about natural climate cycles or anthropogenic--a word that means “caused by people”--climate change.

There are many, many things that affect how hot our planet it, but one of the biggest and most powerful is radiative forcing.  Our atmosphere is a big, protective bubble made up of many gases, mainly oxygen, nitrogen, carbon dioxide, and water vapor.  That bubble reflects some of the sun’s rays back into space, but also lets some through to warm up earth’s surface.  The earth’s surface also reflects the rays back up to the atmosphere.  Depending on what gases the rays meet in the atmosphere, they will either be trapped here on earth or let back out into space.  You may have heard of the greenhouse effect before--the atmosphere acts like the glass in a greenhouse, trapping the sun’s rays to keep our planet warm.  Rather than just letting rays pass through back out into space, these gases cause radiative forcing: they let in more rays than they let out.

The greenhouse effect and radiative forcing, in general, are good things!  Think of how cold and plantless our planet would be if we had as much of the sun’s energy as the rest of space does.  However, the gases in the atmosphere have been gradually changing.  Namely, lots more carbon dioxide, methane, and nitrous oxide have been released, most likely from human activity.  These greenhouse gases in particular are very good at increasing radiative forcing, and as they do, they warm up the planet.  
The Greenhouse Effect, with natural and anthropogenic amounts of greenhouse gases.

The atmosphere isn’t the only place where global warming is caused, though.  Like knocking over a chain of dominoes, a hotter globe means that even more greenhouse gases are released than normal, which further increases radiative forcing.  Melting ice caps mean that less of the globe is covered in ice, which means that more of the sun’s energy reaches the ocean.  Oceans are usually able to absorb much of the globe’s carbon dioxide, but they become less able to do so the warmer they get.  What’s more, as the algae and bacteria floating in the ocean and trapped in the ice die and decompose, they release methane, another greenhouse gas that’s even better at radiative forcing than carbon dioxide!  It’s a vicious cycle, one that scientists call a positive feedback loop.  

An example of a climate positive feedback loop.  Via
Some people like to joke about climate change--you’ve probably heard people mention how they’d like it to be summer all year-round, or that a warmer winter means less snow to shovel.  But the planet warming, even by a few degrees, could have serious consequences.  Melting icecaps and ocean water expanding as it warms could cause sea levels to rise, flooding seaside cities and island nations.  Many plants and animals, already stressed because of their shrinking habitats, aren’t used to living on such a hot planet, and might become extinct.  Even humans aren’t used to living in that kind of heat: farming methods rely on our current temperatures, so a hotter globe could mean food shortages, especially in the poorest parts of the world.  Nearly every aspect of life on earth will be affected by the global temperature rising.  If humans continue releasing as many greenhouse gases as they currently do, scientists estimate that the temperature will rise by about 5 degrees Celsius (about 9 degrees Fahrenheit) by 2100.  This will trigger enough positive feedback loops to turn most of the globe into a desert.
Some effects of a global temperature increase.

From one of my favorite Doctor Suess books, The Lorax. Via
Talking about climate change and its results can be really scary.  Whenever I stop and think about the massive scale of the problem, I feel like there’s nothing that I can do to stop it.  Even if I do things that we’ve always thought of as “good for the planet,” like recycling, driving less, and using less electricity, will it be enough?  Probably not.  Can I single-handedly stop everyone from releasing carbon dioxide, when most of our power system relies on burning coal and oil?  Definitely not.  But the good news is that the most powerful thing to stop global warming is something we can do: we can tell others what we know about the science of climate change.  If enough people care about lowering greenhouse gas emissions and keeping the planet cool, they will make more climate-friendly decisions, and encourage governments and world leaders to do so, as well.   

It will be difficult to change how we live and use the planet, but if enough people care, it’s a change we can make together!

Resources to learn more:

  • Surging Seas, a risk-zone map by Climate Central. See how a rising sea level would affect your neighborhood.
  • Climate Kids by NASA has lots of great articles and games to learn more about climate.
  • Our Time to Lead,'s youth coverage of COP-21, the most recent international climate summit in Copenhagen
  • The EPA offers some suggestions for actions you can take to shrink your carbon footprint.
  • The Greenhouse Gamble, a nifty way to model scientific uncertainty when it comes to complicated issues like climate change, developed by MIT's Joint Program on the Science and Policy of Global Change.
  • Interested in becoming a climate scientist? Come learn more about science, technology, engineering, arts, and math at the Cambridge Science Festival from April 15-24!

E. Rosser is a science writer and mechanical engineer currently wrapping up a degree at MIT. She thinks climate change is the most pressing--and most exciting--challenge facing the world today, and that we'll solve it only through science education. When Rosser's not blogging or in school, she likes to embark on zany building projects and play with her two pet rats, Ellen and Darwin.

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