Thermal lag
Just as a pot of water doesn't burst into a boil the moment you turn on
the heat, the Earth takes a while to heat when you crank up the CO2.

Key Point #1: Climate lags -- Most of the consequences of what we've done haven't happened yet.


I find people tend to be complacent about the dangers of climate change. A common sentiment is, "Before we spend a lot of effort and money trying to fix climate change, maybe we should wait and see if it actually turns out to be a big problem."

It's a seemingly reasonable idea: in most places where people live, the weather has gotten warmer than it used to be, but not drastically so. Winter still comes right on schedule, and in some places it even dumps a bunch of snow. So how can this be a climate emergency that requires an immediate, massive response?

One of the most frightening aspects of global warming, which few people realize, is that there's a time delay for the consequences of our actions to show up. The really catastrophic effects won't become obvious until it is too late to reverse them. The news media have been completely remiss in explaining this to the public. There are two key points about the science which everyone should know: lags, which delay and disguise the effects of our greenhouse gas emissions, and feedbacks, which magnify the effects when they do occur. Put these two effects together, and the science is clear that a "wait and see" approach to climate change is an invitation to disaster.

Let's look at how CO2 works, and why there's a lag in its climate-disrupting effects.



CO2 And Earth's Accumulating Heat

Rising CO2 level
The amount of CO2 in the atmosphere is
rapidly rising because we're taking carbon
from the ground and putting it into the air.
        Image by NASA

Carbon dioxide occurs naturally in the Earth's atmosphere, and it plays a critical role in our planet's temperature regulation (it's a greenhouse gas, meaning it traps heat). Without the greenhouse effect provided by naturally occurring amounts of CO2 and a few other gases, the Earth's average temperature would be a chilly zero degrees Fahrenheit (-18 C), roughly the same as the average temperature on the airless Moon.

So the climate issue isn't about CO2 being good or bad. In the right amount, CO2 keeps our planet from being a frozen, icy world. But like anything, when you have too much of a good thing, it becomes a bad thing.

Since humans started burning coal, oil, and natural gas, we've been taking fossil carbon out of the ground, and releasing it as CO2 gas. As we pump CO2 into the air, much of it stays there, accumulating year by year, adding to what was in the atmosphere naturally. Before humans started burning fossil fuels, the natural concentration of CO2 was about 280 ppm. We've now pushed that up to 392ppm, a forty percent increase over the natural level.

You might expect that a forty percent increase in one of the main heat trapping gases would cause the atmosphere to trap a lot more heat, and that's exactly what's happening. The amount of heat the planet is accumulating every day because of that extra CO2 is so massive, it's hard to put it into numbers that we can relate to. But here's a try. The heat being trapped is the equal to the energy of a million Hiroshima bombs exploding every day on our planet. It's about 50 times the total collective energy consumption of humanity.

Heat energy trapped
The extra heat being trapped because of the CO2 humans
have put into the atmosphere is equivalent to a million
Hiroshima bombs exploding every day, all over the planet.

That energy shows up in a lot of places. It means there's more energy available for melting ice, which is why glaciers are rapidly melting away, all over the planet. There is more energy available to evaporate water from one place, and dump it somewhere else, so global warming means an increasing incidence of both bone-crackling droughts and torrential flooding rains. When that evaporated water in the air condenses, it releases the energy that went into evaporating it, and that's largely what powers storms. More energy in the atmosphere means increasingly powerful, energized storms.

And that's just what's happening. If you've noticed the weather seems to be getting wilder lately, it's not your imagination. The planet is experiencing an increased incidence of heat waves, flooding rains, droughts, intense storms, driven in large part by that accumulating heat, which energizes all of these kinds of events. As that heat continues to accumulate, we can expect events like these to increase in frequency and intensity.

In addition to making extreme weather events steadily more frequent and intense, that stupendous rate of heat accumulation is making the temperature of the planet rise. But the key point is that the increased level of CO2 doesn't immediately translate into increased temperatures around us. It takes decades for the planet to fully heat up in response to an increased level of CO2. That means that we're not the ones who will experience the full planet-warming of the greenhouse gases we release today. Our children are.


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Thermal Lag: The Forty-Year Delay Between Cause And Effect

Why don't we experience the full temperature rise from CO2 right away? One reason is simply that even though there's a lot of heat being trapped, Earth is a big place. It takes a while for all that accumulating heat to warm the whole planet, especially for the oceans to warm. When you set a big pot of water on the stove and turn up the heat, the pot doesn't instantly burst into a boil — it takes some time to heat up. The Earth is covered with oceans that are wide and deep, and it takes decades for all that water to warm up. Right now, most of that extra heat being trapped is going into warming the oceans.

Heat going into oceans
Most of the extra heat being accumulated is going into warming the oceans.
                       Image by scepticalscience.com

The best estimate for the thermal lag delay is that it takes very roughly forty years* from the time we increase CO2 levels for most of warming to occur in response to that extra CO2.

If we think of Earth as that pot of water on the stove, we've just pushed the burner to a higher setting by raising the level of CO2 in the air. The water temperature has started to rise, but there hasn't been enough time for the water to heat up fully in response to the higher burner setting. If we want to keep the pot from getting too hot, we need to turn the burner back down right away. The problem is that instead of turning that burner down, we're cranking it up higher and higher, faster than the pot can heat up in response.


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Aerosols: Masking Half The Warming

There's another factor contributing to the lag, which disguises and delays the effects of our emissions. This one seems paradoxical to many people when they first hear about it.

Smokey aerosol pollution
CO2 isn't the only pollution we're putting into the atmosphere
by burning fossil fuels. There's also a lot of aerosols, smoky particles
that reflect sunlight.

When we burn coal and oil, carbon dioxide isn't the only thing coming out of all those smokestacks and tail pipes all over the world — there's also a lot of smoke going into the air. And some of the gases released by burning later condense into solid smoky particles in the atmosphere. Scientists use the term “aerosols” to refer to all these microscopic bits of solid matter floating in the atmosphere.

(Note: The term “aerosol” means tiny drops of liquid or solid suspended in the air. People call pressurized spray bottles “aerosol cans“ because they spew tiny drops of liquid. When we talk about aerosols in relation to the climate, we're not talking about spray bottles, we're talking about all the gunk that comes out of tail pipes and smoke stacks along with the carbon dioxide.)

Aerosol pollution affects the climate in a number of complicated ways that scientists have only recently sorted out. The overall effect of all those aerosol particles is to reflect a percentage of the sun's rays back off into space, causing a cooling influence on the planet.

By simultaneously pumping two different kinds of pollution into the air, greenhouse gases and aerosols, humanity is inadvertently causing two opposing temperature influences on our planet. We're cooling the planet at the same time as we're heating it. It's kind of like having your home's air conditioning and heat running at the same time, battling each other. But in the case of the Earth, the heating we're causing with greenhouse gases is stronger than the cooling we're causing with aerosols, so the tug-of-war between the two opposing forces has balanced out so far to create only a moderate planetary warming.

Aerosol cooling effect
The short-term aerosol cooling effect is temporarily masking about
half of the long-term warming effect of our greenhouse gases.
                  (Image © British Crown copyright 2011, the Met Office)

The exact size of this cooling influence is still being investigated, but research so far indicates it appears to be very roughly about half the size of the warming influence caused by the greenhouse gases we've put into the atmosphere. So if it weren't for all that aerosol pollution we're releasing, we'd be experiencing about twice the warming effect that we're getting right now. (If we were adding just the aerosols to the atmosphere without adding CO2 at the same time, we would be making the planet colder right now, not warmer.)

At first that sounds like a good thing, that aerosols are cooling the planet. But here's the kicker: aerosols stay in the atmosphere for only a few months or years, while much of the CO2 we put in the air stays there for centuries. The cooling effect from aerosols is short term, but the warming from greenhouse gases is with us for the long haul. Aerosol cooling does not eliminate greenhouse warming, it disguises and postpones it.

Just as with the thermal lag, the aerosol cooling effect is a false friend that's been lulling us into complacency. By postponing most of the climate warming, the lags are allowing us to accumulate a much higher load of greenhouse gases in the atmosphere before the public notices the climate going wacky as a result.


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Already In The Mail: Three Times More Warming

Climate lag
Climate lags: We've warmed the Earth by 0.6 degrees C so far, but the full
warming effect we can ultimately expect from the greenhouse gases we've
already put into the air is 2.4 degrees.

So what's our status right now? How much warming can we ultimately expect from where we've cranked up the greenhouse gas “burner setting“ on the planet? Scientists estimate that between the thermal lag and aerosol-cooling effects, the climate warming we have experienced so far is very roughly about 25% of the warming we can ultimately expect from the CO2 we've already put into the atmosphere.

That is, even if we were to bring the rise in atmospheric carbon dioxide to a dead halt immediately, and hold it steady right where it is today without lowering it, we would still have in store for us three times as much warming as we've already experienced, from the coal, oil, and natural gas that we've already burned.

If we could quickly bring that atmospheric level of CO2 down, we could avoid much of this "on the way" warming. But we're not bringing that carbon dioxide level down, and we're not even slowing the rise. We're pushing it steadily higher and higher, roughly 2-3 ppm every year, adding to the burden of climate change our kids and grandkids will have to deal with.


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More Aerosols Will Only Let The Problem Get Worse

Some people look at this and say, “Oh, the solution to global warming is simple. Just add more aerosols to balance the warming!” Unfortunately, it's not that easy. There are at least three reasons why this is a very bad idea. First, it does nothing to solve ocean acidification caused by increasing CO2. Second, it could disrupt rainfall patterns (failure of the Asian monsoon, for example, is a possible consequence that would imperil the food supply for a billion people). And third, most important, by attempting to solve a long-term problem with a short-term solution, it lets the underlying problem get worse and worse.

We would be using a short-term cooling effect to mask a large and growing package of long-term "on-the-way" warming. That's like a person who's lost their job paying all their expenses with credit cards. It can help for a very short time in a pinch, but doing it for any length of time magnifies the underlying problem into disastrous proportions.


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The Urgent Need To Reduce CO2 Levels, Not Just CO2 Emissions

The most important lesson in all of this is critical need to get the word out: we urgently need to reduce not just CO2 emissions, but the actual CO2 level in the atmosphere as quickly as possible.

One of the biggest reasons for the general complacency about climate change is that nobody has told the public that most of the effects of our emissions are being disguised and delayed by climate lags. Without this critical piece of information, it's impossible for people to appreciate just how urgent and dangerous our situation is. It's essential that we get the word out about this, and critical that the media start explaining it to the public.

The public for the most part can't yet directly observe the massive effects we are causing on our planet, and nobody explains to them that the reason why is that most of the warming from the greenhouse gases we've released is still on the way. People are left to wonder why they haven't yet seen the drastic change in their daily weather that they've been expecting from all the talk of global warming.

So people conclude that there is no crisis, and there's little public support for the kind of action that will re-stabilize the planet's energy balance. Meanwhile, every year we add to the load of greenhouse gases in the atmosphere, increasing the burden of planetary warming our children will face.

It all adds up to a pretty scary situation, but as we'll see, it's only the beginning of our predicament.




Next: Key Point #2 - How climate feedbacks threaten to magnify the warming when it does arrive.











*"it takes very roughly forty years..." We've oversimplified that somewhat for clarity. The actual estimate for the thermal lag is 25-50 years for 60% of the warming to be realized (the exact length is determined by rate at which warm surface ocean waters mix with deep cooler layers.) The mid-point of this range is 37.5 years, and rounding gives 40 years.



** "very roughly about 25% of the warming..." This study calculating a further 1.8 degrees of warming we can expect from the greenhouse gases we've already put into the air is based on calculating the expected temperature rise if we could freeze the level of greenhouse gases in the air at its present level, leaving out the temporary cooling influence of human-made aerosols.

This number is larger than other studies' estimate of approximately 0.6 degrees of "on-the-way" warming. The studies giving the lower figure calculate the expected temperature rise if we froze atmospheric levels at today's concentrations of both greenhouse gases and aerosols. Since human-made aerosols are blocking about half of the warming effect we would otherwise be experiencing from the human-made greenhouse gases in the air, this results in a lower estimate for expected warming.

But aerosols tend to fall out of the atmosphere much more quickly than greenhouse gases (over weeks to months for aerosols, compared to decades to centuries for most greenhouse gases). And many countries are enacting clean-air regulations that reduce aerosol emissions. So leaving aerosols out of the calculation likely gives a more realistic approximation of the expected warming from the human-made greenhouse gases already in the atmosphere.