We all know what that is. It's the magical process by which plants turn solar radiation into energy and the other stuff they need to survive and grow. Cut off sunlight and photosynthesis stops. Stop photosynthesis and plants die.
Remember the story about the mass extinction of the dinosaurs? They existed for millions and millions of years. One day a big bad asteroid slammed into the Earth, lots of dust got thrown up into the atmosphere and blocked the sunlight. First the plants died off. Then the plant eaters died off. Then the carnivores died off. Death just worked its way up the food chain. Bottom line: kill enough plants and a lot of animals die. That's just the way things work.
Even if you didn't eat plants, you still need them if you breathe oxygen. That's because the first step in photosynthesis uses the energy of sunlight to split water molecules into its component atoms of hydrogen and oxygen. The plants don't need the oxygen during the day. It's a waste product as far as they are concerned. They blow it off into the atmosphere just like we blow off carbon dioxide. That's a good thing for us and any other animal that breathes oxygen.
So what's this got to do with global warming?
Here's something you may not have known about photosynthesis: it only works over a limited temperature range. You are probably not surprised to learn photosynthesis doesn't work well at temperatures where water freezes. You are also probably not surprised to learn photosynthesis doesn't work well at temperatures where water boils. You might be surprised to learn that photosynthesis stops at a temperature well below the boiling point of water. The magic number? 104 degrees Fahrenheit, or 40 degrees Centrigrade.
It turns out that is a number that is not compatible with a lot of life froms. In humans, a temperature of 104 degrees Fahrenheit (40 degrees Centrigrade) leads to heat stroke. This is a potentially fatal condition. Heat stroke can kill you in a matter of minutes. Humans have gotten around this problem by expanding their ability to operate in broad temperature ranges through the use of technology. We have clothing, heating, air conditioning, and a range of insulating technologies. Left to their own devices, however, plants don't have any of those options. Plants are a bit heartier, so they can actually go days without photosynthesis. But they can't last for weeks.
This would be interesting only to academics except for the fact that temperatures of 104 degrees and higher are starting to crop up in more and more places as the average temperature of the planet's surface increases. That's why this is important. Most discussions about global warming talk about average temperatures. If you think about it, it should be obvious those averages are calculated based on temperature extremes that go above and below the average. Sometimes the range is pretty large.
Remember the heat wave that crippled Europe in 2003? That lasted for almost two weeks. Temperatures reached 104 degrees Fahrenheit in France, and 105 in Germany. About 35,000 heat related deaths were recorded that summer. It's understandable that newspapers would focus on the human toll of these heat waves, but they also had a huge impact on crops.
These are pretty staggering numbers in staple crops used for cereals and feeding livestock. The impact of these crop losses are felt far beyond the immediate loss of the plant material. Side effects include soil erosion and flooding. This is to be expected. However, one stunning finding reported by the BBC was that at those high temperatures plants become net producers of carbon dioxide, dumping millions of tons of carbon dioxide into the atmosphere.
Putting all the data together, the headline figure is that, overall, European lands were 20% less productive than during an average year.
The really surprising finding came with the calculation that during the heatwave, European plants and their ecosystems were putting more carbon dioxide into the air than they were absorbing.
During an average year, the net effect is that European plants absorb around 125 million tonnes of carbon (MtC).
But in 2003, according to this analysis, they released 500 MtC to the atmosphere.
By comparison, global emissions from burning fossil fuels amounts to about 7,000 MtC; by giving rather than taking, European plants were adding about 10% to the global total. [emphasis added]
"This shows that short-term climatic events such as the 2003 heatwave occurring over regional areas like Europe can have major effects on the climate globally," commented Julia Slingo.
Studies published in Nature looking at this heatwave and associated events have reached even more alarming conclusions about what the weather will be like by the end of this century:
"In fact, our predictions say that if we carry on without serious attempts to reduce greenhouse gas emissions, then we could be experiencing a summer like the one we had in 2003 in Europe every other year."
We have seen the impact of such extended drought and heatwaves in the United States. The 1930s were very hot and very dry. Coupled with poor land management, this contributed to the famous Dust Bowl years. One consequence of that was a radical and permanent shift in the economic makeup of American farms. Although the percentage of Americans working as farmers had been steadily decreasing since the early 19th century, the average size of the farms had stayed relatively stable up until the Dust Bowl years. After that time, the number of farmers plummets and the size of farms skyrockets. This is when we moved from a system of family farms to large scale factory farming.
The current heat waves are now occuring in a time dominated by factory farms. Even with all the technical advances, the impact is still significant. There is no way the European economy could maintain its current standard of living and absord 20% losses in farm productivity every other year.
The European heat wave of 2003 was notable for its length, but it is not an isolated incident. When you start looking around the globe for extreme reports, you find they are not as rare as you might expect. Recently, extreme temperatures of 104 were reported in Austin, TX. Similar temperatures were also reported in Houston. Temperatures as high as 105 degrees were seen earlier this year in New Zealand. A string of similarly hot days were reported in Australia and more were predicted.
It might be easy to dismiss these as "merely extreme" examples on top of a general expectation that average global temperatures will increase by about 3 degrees over the next century. 3 degrees doesn't sound like a lot until you start looking at models for the extreme data. That's where things get ugly.
The conclusion of these studies is that the extremes will increase faster than the average.
A comparison of simulated 100-year return values for the present climate with observations (station data and reanalysis) shows that the ECHAM5/MPI-OM model, as well as other models, overestimates extreme temperature values. After correcting for this bias, it still shows values in excess of 50°C in Australia, India, the Middle East, North Africa, the Sahel and equatorial and subtropical South America at the end of the century. [emphasis added]
Here's what that looks like (images from the complete paper):
Note: This is after correcting for overestimates in other models. In other words, this is a conservative model of extreme temperatures expected by the end of the century. Everything in orange and red is not compatible with photosynthesis. That's bad.
This isn't going to happen overnight. In fact, the trend is already clearly developing. According to this model, the Netherlands won't see these sort of extreme temperatures on a regular basis until the end of the century. However, they are already seeing this in parts India. We can expect to see these temperatures on a regular basis in the US in the next 25 years.
The impact of these sustained extreme temperatures will be catastrophic for life as we know it. We're not just going to lose food production, we will also see plants dumping carbon dioxide into the atmosphere. That will just make things worse. The economic impact would pale in comparison to the toll on human life.
Unfortunately, facts have never stopped the global warming deniers from pushing their faith-based positions. They don't want to think about stuff; they go with their gut. They feel they are right and that is good enough for them. I think we should respect their feelings. In the future, if anyone wants to seriously debate the threat of global warming I suggest we agree to have that debate on one condition. We do it in a room that is 104 degrees Fahrenheit (40 degrees Centrigrade). The deniers may not change their minds, but at least we won't waste a lot of valuable time arguing with them before they succumb to heat stroke.
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