This year the CO2 in the atmosphere reached the level of 392 ppm. The level of CO2 for the past 800,000 years was at its highest about 280 ppm, which is where it was before the industrial revolution began around 1800. By 1950, the CO2 level was at 315 ppm and rising at about .5 ppm per year. Now it is rising at about 2.5 ppm per year. So the rate of increase has itself increased. Unabated, we will be at 415 ppm by 2020, and about 470 ppm by 2050.
OK, well and good, but what does that really mean? We have to look at truly ancient climates to get possible answers to that question. We have to look past the relatively recent cycle of ice ages and interglacial periods of the last 800,000 years. We need to look at the ages where CO2 levels were about what they are now and where they might be if the CO2 levels are allowed to rise unabated.
If we go back about 3.5 million years we get to the climate age called the Pliocene. The Pliocene lasted from approximately 5.5 million years ago (mya) to about 2.5 mya. Over this time, the continental drift caused the Mediterranean Sea to be formed and the Isthmus of Panama to rise and connect North and South America.
The seas were warmer and the climate was +2.5C (+4.5F) warmer than today. There was no Greenland Ice Cap, and no Arctic Ice at all. The oceans were 25m (80ft) deeper than they are today. The CO2 levels were about 390 ppm.
Since we are already at the Pliocene carbon dioxide levels, the question really is "what is going to prevent the duplication of the Pliocene climate from being recreated?". A second question is "how long will it take for a Pliocene like climate to establish itself?"
Let's look at the first question. At this time, no process has been identified that will likely prevent the establishment of a Pliocene like climate. The identified feedbacks mostly amplify and accelerate current warming trends. Those feedbacks include 1) loss of Arctic albedo (ice reflectivity), 2) melting permafrost adding carbon dioxide and methane to the atmosphere, and 3) release of methane from shallow undersea formations called clathrates. Of course, mankind is still accelerating its burning of fossil fuels worldwide.
The climatologists differ significantly on their estimations of how long for warming to take effect. The disturbing feature of their estimations is that for the past ten years their estimations have gotten progressively worse. Each time they update their estimates, they are more dire. The ocean levels rise higher and faster. A recent update in Ice News, said that oceans may rise up to 5 ft by 2100.
Can that be right? 5 ft? That would flood much of the food producing areas of the world located in river deltas. The Nile delta, Mississippi delta, Ganges delta (Bangladesh), Mekong Delta, Danube delta, and so many more would be mostly underwater if that happened.
For that to happen the Greenland Ice cap would have to start melting at a very fast rate. To rise 60 inches by 2100 it would have to rise at over 1/2 an inch per year, or about 150mm per year. We have been rising at about the rate of 2.5 mm per year in recent years. The climatologists are expecting Greenland to start melting at a significant rate in the next decade or two. The oceans may only rise 6-12 inches by 2050. What can cause Greenland to start melting real fast?
To answer that we have to look at the position of Greenland. The Arctic Ocean is to the north. Much of its weather comes from the north and northwest which have been perpetually ice covered for hundreds of thousands of years. Soon, though, the Arctic Ocean will be ice free during the summers, and will be absorbing sunlight and getting warmer. As that happens, then Greenland will be surrounded by open ocean at above freezing temperatures. No matter what direction the weather comes from it will bring above freezing warm air to Greenland for a season each year.
With each passing year, the Arctic Ocean gets warmer from absorbing sunlight. And each passing year, the melt season for Greenland gets longer and warmer. Greenland melting will go into overdrive. It will go into hyper-melt mode. When that happens, then we will likely start seeing the seas rise at 100 mm to 200 mm per year.
Is this for absolute certain to happen? Unfortunately, our knowledge is still developing, and we don't know everything. As of now, no one can point to any natural process that can stop this. Even if mankind stopped dumping CO2 into the atmosphere, these events are likely to happen. Maybe if mankind decided to remove CO2 from the atmosphere to lower levels to 350 ppm or lower, that might work.
The second question was "how fast". Even if oceans rise only 4 ft, or 3 ft, or 2 ft, does not mean that the processes won't continue and give us the same result. For some reason, the year 2100 has been used as projecting the results of global warming trends. However, the global warming will not stop at 2100. In fact, the accelerated pace of ocean level rising that is expected to occur from 2050 to 2100 will still go on and accelerate even further.
Remember the Pliocene oceans were 80 ft deeper. Greenland was free of ice, and the Antarctic had much less. The estimation for how long it will take the whole of the Greenland ice cap to melt (assuming mankind does nothing to reduce CO2 to 350 ppm or less) varies for 2,000 years to 300 years. The estimated 5 ft of increased ocean rise will mostly come from Greenland. That will represent about 20%-25% of Greenland's mass. At that rate, then Greenland's ice would be gone around 2400.
Antarctica will have started melting, so a rise of 30 ft to 40 ft by 2400 seems reasonable, maybe more. How long to reach an increased depth of 80 ft? That is difficult to answer because the climate dynamics that will be created in just the next hundred years may be very different. Ocean currents may change. Ocean temperatures will definitely change. Ocean chemistry will change. All these can effect the carbon cycle and the water cycle, and thus effect climate. Hopefully, processes will be altered or uncovered that will slow down, halt, or reverse the warming climate trend caused by higher CO2 levels.
Global Warming is undoubtedly the greatest challenge that mankind can face. People have difficulty planning ahead even a few years. A decade is beyond most people's ability. To cope with Global Warming people have to deal with decades and centuries. People live in cities mostly, and are cut off from the natural world around them. Even when it is nearby, they tend not to notice. Lake Michigan was once a very cold lake to swim in, even in August. Now it is wonderfully comfortable by July. It has increased in temperature 12F since the 1960's. The changes are around us. The changes will be more significant in the future and probably much less welcome.
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