While the publication of Rachel Carson's "A Silent Spring" in 1962 may be fairly considered the foundation moment of the modern day environmental movement, the first Earth Day, held 44 years ago in 1970, and observed this past Tuesday, was also a turning point. Coming at a time when the Cuyahoga River in Cleveland caught on fire, and smog alerts in Los Angeles were far from exceptional, Earth Day crystallized concerns around clean air and water, and combined with the OPEC oil boycott of 1973 (ironically), began the long march of efforts to reduce dependency on foreign oil, and oil and other fossil fuels in general, in favor of more environmentally-friendly renewables.

That long march still has a way to go, but there is encouraging news around the economics of renewables. Up until very recently, it was vastly cheaper, in terms of dollars and cents, to burn oil and coal rather than harvest energy from the sun and wind. When those two trend lines finally converge and overlap, a new world will indeed be at hand. It's one filed with potential opportunities for jobs and investment.

That progress is coming at a fortuitous time, as a recent report from the United Nations Intergovernmental Panel on Climate Change (IPCC) points out.

This group of science and environmental experts has been studying climate change for some time now and while its conclusions have been attacked on and off as "bad science" it's a little hard to argue, at this stage, that humans are indeed pumping more and more carbon dioxide into the atmosphere and warming the planet gradually. In a way, the gradualness of the process is part of the perception problem. No one who lived through this past winter in Vermont would seem to be on firm ground arguing that the planet is inexorably warming. This is a slow motion process, playing out over years and decades. No galvanizing "9/11" moment here.

But the evidence does clearly point to continued warming, perhaps enough to threaten the viability of coastal cities and the fertility of certain traditional agricultural breadbaskets. What's intriguing and adds to the complexity of this subject is that climate change - in addition to its slow motion character - is also having varying impacts on different parts of the world.

Many of those impacts depend on differing nation's priories around economic development. It will be hard, if not impossible, to make major headway until the developing nations - which include powerhouses like China, would-be powerhouses like India, and a host of smaller nations clamoring to get rich first before getting green later - create a consensus that just because the developed (and relatively rich) world leveraged their wealth through access to cheap fossil-based fuels, they will not have the same option.

If all the developing nations do is follow in the same path as the U. S. and the rest of the developed world, reaching any kind of target sought by UN officials is hard to imagine. That may not seem fair, but the connection between fossil fuels and climate change was not remotely part of the picture 40 or 50 years ago. Now we know more.

Closer to home, we still see continued tension between economic growth and reducing reliance on fossil fuels, widely considered to be the source of much of the carbon dioxide and other greenhouse gases held responsible for a warming planet. That tension plays itself out most clearly in the current furor over fracking and the Keystone Pipeline.

Fracking - short for hydraulic fracturing - is a brilliant bit of engineering wizardry. Invented originally in the late 1940s, it uses a horizontal drilling technique to access and retrieve vast stores of underground gas and oil trapped in shale rock deep underground, far deeper than the underground water we use. But concerns have long persisted that the process contaminates this drinking water, as well as possibly being linked to underground earthquakes and jeopardizing the stability of the Earth's outer crust.

At the same time, fracking has been an economic boon of the first magnitude for the U.S., a global leader in this technology. It's also fair to say that if fracking had not been perfected to the point it has, and all the jobs and less expensive natural gas had not been accessible to the economy, we would still be talking about a flatlined economy that was going nowhere. The question is not about banning fracking - as Vermont's legislature did a few years ago, at least for now and which was an easy call since there isn't much natural gas or anything else worth fracking for here - the question is about crafting sensible rules and regulations to govern the practice and punish irresponsible drillers who take the short cuts and leave behind an environmental mess once they are finished. That should not be an impossible task.

The Keystone Pipeline, proposed to run from Canada through the Great Plains States to the Gulf of Mexico to allow Canadian oil to be shipped overseas, is a massively complex issue as well as a political headache of the first order for the Obama administration. Deny the permits to build the pipeline, which the U.S. State Department has jurisdiction over, and the Canadians will, in all likelihood huffily export it overseas anyway. The heavy "tar sands" quality of the oil will go up in smoke somewhere. While the economic and job creating impact of the project has probably been overstated by its most ardent backers, it's not insignificant either. But whether building it means it's "game over" for the environment, as James Hansen, one highly respected scientist has put it, may be an overstatement also. In any event, in the short term, and with a fall mid-term election coming up, the timing is awkward for the administration, leery of losing what remains of the green cohort of its coalition. This case also sums up the complexity that attends to the entire climate change question. It's understandable the administration is playing for time. There's no easy answer, and we don't have one either.

Climate change is complex. On balance, its hard to argue the climate isn't changing. But as the recent IPCC report shows, climate change is a problem that interacts with others, and the severity and likelihood of storms like Irene and Sandy may be dictated more by that interaction, than in isolation. That insight may drive a new phase of the discussion around climate change and what to do about it.