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Don Paul: The main reason the world is warming is ... us

Don Paul

Global warming continues, and has been going on for decades. Every location on the globe is not affected equally, but for most locations in the northern hemisphere, the trend is undeniable.

In the lower 48, only a small area in the north central states has seen a bit of cooling since 1970 in the summers. Globally, the mean monthly temperatures have been rising month after month.

In the temperate zone, summers are getting longer and winters are getting shorter. Globally, temperatures have been running above historical averages month after month.

For football fans, even football season has been getting warmer.

In some of the hottest places, the heat is getting worse. Check out Phoenix.

In our back yard, the trend has been much less pronounced, thanks to the moderating effect of the lakes, especially Lake Erie.

However, that moderating trend is confined mainly to daytime hours, when the lake breeze is more pronounced. At night, it’s a different story. We are warming more demonstrably.

The fact of the matter is, climate models demonstrate the main reason we are warming is…us. Human activity is the primary culprit, and has been for decades. Ocean conveyor currents can shift from time to time, and atmospheric/sea surface interactions can cause periodic warming or cooling.

Still, climate modelers showed the evidence several years ago to colleagues and me at the National Center for Atmospheric Research in Boulder, Colo. When you bring carbon dioxide levels back down to levels of we had around 1900-1910, even when those modelers pumped up solar input to the max, and pumped up all natural warming mechanisms up to the max, the models show the globe would have been in a slight cooling period since at least the start of the 20th century. That is, if carbon dioxide had stayed at those lower levels we would not have a warming climate at this time. Carbon dioxide is up more than 40 percent since the start of the industrial revolution. Yes, it’s a trace gas, but it has an absolutely proven strong greenhouse effect and a long “shelf life” in the atmosphere. More potent methane has a much stronger greenhouse effect, but its “shelf life” is much shorter than that of carbon dioxide.

Water vapor is by far the most prominent greenhouse gas. So, how can a trace gas lead to so much warming? Besides carbon dioxide’s own strong greenhouse effect, the warming climate puts more water vapor in the atmosphere by way of evaporation. So, the increase in carbon dioxide leads to an increase in water vapor, in addition to carbon dioxide-driven greenhouse warming. And the warming also puts more methane in the atmosphere by warming the oceans, allowing more methane to rise from the sea floor, as well as from our melting permafrost to the north, where warming has been greatest precisely as modeled back in the 80s. Lots of methane, of course, gets sent into the air from livestock, though that is also human activity. In sum, climate scientists and atmospheric physicists can find no other explanation for the ongoing warming other than human activity.

We would be warming much faster on land were it not for the vast capacity of the oceans to absorb excess heat and carbon, as a heat and carbon “sink.” Eventually, the oceans will come closer to heat and carbon saturation and will gradually convert to a heat and carbon “source.” In the meantime, the extra carbon in the oceans is causing acidification which is deadly to many coral reefs.

The persistence of these feedback mechanisms mean there is no quick off switch to global warming. We can work to slow it, but the idea of stopping it in the decades to come has little scientific support. Slowing definitely counts, because it can make a huge difference in how much sea levels rise, and how much mitigation of coastal flooding can be accomplished by costly engineering with barriers and floodgates. Even now, the southeast coast of Florida sees more frequent flooding with high tides, complicated by the slowly rising sea levels.


Due to the already significant impacts of warming, society must now weigh the very high costs of those engineering projects versus the much higher costs of letting nature take its course. Efforts to reduce the greenhouse gas load are important, but if we’re waiting for those efforts to reduce the profile of damage from a warming climate, it’s going to be a long, destructive wait. There will be tough choices for our vulnerable coastal population centers in the near future.


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