Bjorn Lomborg is an unusual kind of academic. He's unusual in the fact that political ideology means less to him than utilitarianism. For example, there are plenty of professors in the faculty lounges across the United States who will support faddish social causes that wouldn't promote as much social good as other causes, but they do so because they implicitly put their political ideology ahead of their ostensible purpose to maximize social welfare.
Anthropogenic climate change (global warming) is the most prominent example. It's almost exclusively the concern of the intelligentsia living in post-industrial markets. The reason why emerging markets are so opposed to global warming is because the policy prescriptions would disproportionately hurt their economies the most.
The reason is simple. The modern economy relies on cheap energy. And the cheapest forms of energy (coal) tend to be the most polluting. Developed markets like the United States and Western Europe already have the capital wealth in place to decrease their reliance on dirty forms of energy like coal power (albeit at extraordinary financial cost). But markets like China, India, and Brazil don't.
Ostensibly, the goal of the green lobby is to reverse global warming to create a sustainable environment that will benefit all of society. There is no doubt that clean energy is a public good. But it takes a lot of money to have clean energy. And that's money emerging markets don't have.
If the stated goal of the green lobby is to maximize the social welfare, then global warming shouldn't be their number one priority. This is where Bjorn Lomborg comes in. He posits that in a world of limited resources, we have to prioritize public policy that does the most good for the least amount of money.
Things like promoting increased food security through micronutrient supplementation/fortification (distributing mineral/vitamin tablets), increased access to high yield GMO crops, and nutrition education can greatly benefit humanity by preventing malnutrition and starvation in countries that are extremely poor.
Spending money on more expensive sources of energy provide very little benefit (which goes mostly to developed markets and the people who need it the least). Norman Borlaug, who pioneered GMO crop development, is estimated to have saved a billion people from starvation. Increasing electricity generation by solar from .01% to .5% would cost the US 1000 times as much money as was spent supporting Borlaug's research, but it wouldn't come close to saving even a thousandth of that number.
The bottom line is social welfare is about human lives. And saving human lives is vastly more beneficial than making human lives marginally more comfortable.