Musing on the Benefits of CO2

So what role does CO₂ play in the climate picture? This section is largely my opinion based on a big picture look at the earth’s history. I do believe that CO₂ increases do lead to higher temperatures. However, those temperature increases based on CO₂ alone will be moderate (as discussed earlier). Moderate global temperature increases are hugely beneficial. Growing seasons become longer and more arable land becomes available. Remember, during the Medieval Warm Period, the Vikings settled and farmed Greenland (try to do that now). Another obvious benefit of rising CO₂ levels is the greening of the planet. Existing forests are healthier and vegetation has been establishing footholds in previously low vegetation environments (deserts, high steppes, etc.).

CO₂’s contribution to global temperature is real. But in general, rising CO₂ will only contribute to the rise in temperature when solar activity increases or will temper the drop in temperature when solar activity decreases. And for that we should be thankful. Any 0.1 °C increase due to CO₂ increases, means the depths of the coming GSM is 0.1 °C warmer than it could have been.

The ice age we are currently living through is once again characterized by longer durations and low CO₂ levels. Obviously CO₂ is not the only factor affecting the climate on this time scale but there is a qualitative correlation present (i.e.: low CO₂, longer and/or deeper ice ages and vice versa).  The red dataset is the updated temperature from the same researcher (C.R. Scotese) who generated the original blue data.  I included the new data after coming across some discussion suggesting the blue temperatures were out of date. The new temperature plot doesn’t change the discussion points.

CO2 has played an important role in regulating temperatures over the last 800,000 years. As discussed earlier (re: the Milankovitch cycle discussion), the low CO2 levels in the depths of the ice age lead to severely stressed plant life and widespread desertification. The atmosphere becomes loaded with dust particles that eventually settle on the ice. Over time these dust particles darken the ice, making it easier to melt. The planet goes through an interglacial warm period roughly every 100,000 years. We are currently living through the Holocene Interglacial. A number of factors go into initiating these interglacial warm periods but they always occur when the planet’s orbit is at a maximum in its orbital eccentricity cycle. The low CO2 concentration induced dust helps the melting process (leading to rapid temperature increases). As the temperature rises there is some positive feedback from the rising CO2 levels but there is no evidence of the runaway temperature effect promoted by the “Global Warming” crowd.

Another example of CO2’s potential benefit can be seen by focussing in on the deep ice age/interglacial warm period cycle.The Holocene temperature profile is considerably different than any previous interglacial warm period. In general, temperatures rise quickly out of the deep ice age, peak (often higher than the Holocene peak) and then drop quickly back into the deep ice age. The Holocene deviated from that pattern. The temperatures peaked but instead of dropping quickly, they have declined at very moderate rates. Around 7,000 years ago, atmospheric CO2 concentration rises accelerated. Although the increase was relatively small, it may have been enough to keep the planet above whatever tipping point drops the temperature to ice age levels.

The historical temperature data (Vostok ice cores) in these charts has been normalized to the point where the temperatures begin rising out of the deep ice age. The first chart includes the entire cycle (covering the last 420,000 years). The second chart focusses in on just the interglacial warm periods.

Cycles 2, 3 and 4 have very similar profiles (especially 2 and 4). Cycle 3 had an exceptionally short interglacial warm period but followed the same general pattern through the deep ice age period. Cycle 1 (the Holocene, the current interglacial we are living through) did not peak and decline immediately. The Cycle 1 profile looks a bit more like Cycle 5 (the oldest cycle) which does not have a sharp peak and a quick decline. All of the previous cycles peaked at more than 2 °C above the Holocene maximum which occurred around 5,000 – 6,000 years ago. And guess what, CO₂ played no role in those higher temperatures and the planet had no problem surviving those temperatures. So if we are lucky, we may be in a cycle that continues to mirror Cycle 5 (but at a lower temperature). If you go back to the discussion on the Milankovitch cycles, you can see that the insolation at 65° north actually stops dropping and rises slightly before dropping again into another insolation low that is associated with an eccentricity low (which has always resulted in a deep ice age). Given that we have not already dropped into a deep ice age, we may have another 20,000 years of generally warm climate with the same ups and downs that have characterized the Holocene to date.

So is it possible that the CO₂ increases over the last 7,000 years kept us from dropping into a deep ice age? That scenario is illustrated on this graph:

The early Holocene temperature decline may have been headed towards that time in the cycle where the drop into a deep ice age is accelerated. That tipping point is different in every cycle so we don’t know exactly where it resides. We do know the tipping point was higher in all of the previous cycles and we know we’re still above the Holocene tipping point (thankfully). If the tipping point is the -1 °C temperature anomaly level (purely speculative), we could have already been headed for that deep ice age and today’s society may not have come into existence. The CO₂ increases in the mid-Holocene may have been enough to boost the temperature slightly and keep us above the tipping point. And that is definitely a possibility since a 20 ppm increase beginning at 260 ppm is much more effective in raising global temperatures than a 20 ppm increase beginning at today’s 410 ppm. Especially if you believe the current IPCC computer models (which I don’t). The late Holocene temperature decline would intersect that 1 °C level around 4,000 years from now. Combined with some additional heating from the current levels of CO₂ and our position in the Milankovitch Cycles, we should be able to avoid a deep ice age for an extended period of time.

This last portion of this CO₂ benefit discussion does contain some speculation. But it is not out of the realm of possibility. And you don’t have to take my word for it. Here’s a quote from Bill Nye’s interview with Tucker Carlson on February 27^th, 2017 that expresses that same sentiment. In response to a question about how long it would have taken to reach our current temperatures without human influence (i.e.: CO₂), Bill stated:

“It’s not clear that it would have happened. In other words humans have changed the climate so drastically that we’ve almost certainly avoided another ice age. There would have been another ice age, ain’t gonna happen, ‘cause of you and me.”

I wouldn’t have used the word drastically but whatever. Overall, I would think that Bill should be grateful that CO₂ kept us out of an ice age (which would have been and could still be devastating). His answer is a bit strange given that “It’s not clear that it (referring to the temperature rise over the last century) would have happened” is not that representative of so called settled science.

To summarize, CO₂ is not a pollutant and CO₂ is absolutely essential to life on this planet. We should be thankful for the benefits CO₂ provides us.