I don’t understand your first objection. At no point in the text did I say, or imply that the population increase was due to modern medicine. This is a common misconception, but I’ve been aware of it for a long time and it is not part of my argument.

If, instead, you are actually objecting on the grounds that you DO believe that the population increase was due to modern medicine, then I would have to say that “you’re wrong”. People were perfectly able to live long lives and achieve lower rates of infant mortality before modern medicine became widely available. The real change brought about by modern medicine is healthier people (most easily apparent in the increased height of recent generations), and an increased quality of life. The population increase due to modern medicine is marginal at best, and there are many statistical studies that will back this up.

Your second objection is scientifically misplaced. A marginal increase in CO2 (100ppm may be 30% of total CO2, but it’s still a very small part of the atmosphere) has only a marginal effect on the growth of plants, whereas it has a much more significant effect on the temperature. Moreover, people who study plant biology will tell you that the amount of CO2 is less important than the ratio between gases, and changing those ratios will affect different plants in different ways. That is to say, increasing the CO2 doesn’t necessarily increase the growth of all plants uniformly, but will aid some more than others. This isn’t a huge problem, except that if it is done too quickly (and in geological time, 150 years falls under the category of “too quickly”) it can dramatically shift the equilibrium points of the biotope, which leads to biodiversity loss.

Your point about temperature also misses a major point about how climate and food production are linked. Warmer doesn’t necessarily equal better. It might surprise you to learn that very little of our food is grown in tropical climates, instead it is mostly grown in temperate climates. Why? There are several reasons but the two main ones are (1) our main food crops were indigenous to temperate climates, this is mostly due to the types of flora and fauna that are native to certain climate zones. You will also notice that all of our domesticated animals are native to temperate climates, and this was important to the development of agriculture. The reason that most of our food crops are native to temperate climates has a lot to do with the soil, and also (2) the climate – temperate climates are more stable and have predictable rainfall patterns. Sure, a lot of tropical environments receive a lot of annual rainfall, but it is very unpredictable making it difficult to plan the kind of industrialized agriculture which is in fact the real reason for our population growth.

A temperature increase has the potential to make arable large parts of land in northern Canada, Scandinavia, and Siberia. However, this is by no means guaranteed. There is no guarantee that the soil will be suitable for farming, and even if it is, those parts of the world have almost no infrastructure (save for the trans-siberian railway) for transporting the food. Moreover, the loss of arable land due to desertification in areas of the world which will become too hot to reliably grow food will more than outweigh the gains.

I encourage you to read further on these topics, both on this website and elsewhere. For now, I refer you to the Koppen-Geiger climate chart which can be found here:(http://www.danielyeow.com/2009/the-earth-debate-part-1/) to emphasize the point that suitability for habitation isn’t a linear function of temperature, but is a chaotic function of many variables. The real point being that we should try as hard as we can not to mess with it, rather than coming up with completely unscientific reasons that “more CO2 would be better”. (I say “unscientific” because an understanding of how global food production works, combined with the peer-reviewed literature would suggest that the opposite is the case).

The planet is becoming more inhabitable than at any other time. In the last 50 years human population went from 3B to 7B, a 133% increased, matched by our food supply increase, matched by worldwide crop yield increases, partially brought to us by a 30% increase in CO2 in our atmosphere. Objection one, the population went up because of modern medicine. Answer, no, that caused demographic changes within the population, like longer life expectancies, and lower infant mortality. Unless you can show me pics of 100s of millions of third world double wides from 50 years ago, I’m going to have to serve you the truth, 2000 calories a day 50 years ago, 2000 calories a day today, the population increase was brought about by the food supply increase. Objection two, the crop yield increases were brought about, by hybrids and better plant breeding. Answer, yea, in an atmosphere that has 30% more CO2. The only thing that is making our world more habitable than the CO2 increase, is the temperature increase caused by the CO2 increase. Look at a world temperature map for crying out loud. No sense pretending we grow our crops in the dead of winter, and if it gets any hotter, we won’t be able to grow anything at all. The truth is that there is a vast frozen stretch of land across northern Canada, Europe, Asia.