Maine study finds potentially disastrous threat to single-celled plants that support all life

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12. Other ideas:

The problem is too abstract;
The effects are apparently well into the future;
The effect is just being noticed;
The fix isn't known at this time.

Humans have something called a "hyperbolic discount function", that arises from our evolved brain structure:

Communicating Future Threats

Why is it so difficult to generate concern for events that are seen as belonging to the future even though their consequences may be dire? It happens because of the way we're wired.

Millenia of natural selection favoured people who responded immediately to threats or rewards. Individuals that did not immediately run from the tiger were more likely to become the original Darwin Award winners. This selection reinforced our responses to immediate and clearly understood rewards or dangers. The further away in time the reward or danger was, the lower our response to it became, because its influence on our survival was correspondingly less. Even if we waited to run until a distant tiger got closer, the chances were good that we would escape anyway, so there was no need to leave our meal just yet.

This idea is known as the "discount rate". It's the same concept used by banks, where the present value of a future event is discounted depending on how far in the future it will happen. While banks use a linear discount rate (expressed as a percentage), there is strong evidence that human beings use a more complex function that comes from different parts of our brain. The more primitive parts (the brain stem and limbic system) are concerned with immediate survival and emotional responses. They are much less capable of long-term evaluation, but provoke the strongest reactions to pleasure or fear. The neocortex, on the other hand, is our thinking brain. It analyzes, predicts and plans for the future, but has more limited access to our emotional triggers.

As a result, immediate threats or rewards that require no deep analysis tend to activate the "older" portions of our brain and prompt very strong responses. More abstract threats and rewards identified through the analytical capability of our neocortex don't activate our limbic system, and so usually prompt a much less intense reaction. Immediate, concrete concerns always strongly outweigh distant, abstract ones. The discount function is called "hyperbolic" because it falls off very rapidly at first, then flattens out as time passes. Events that are very near term evoke a sense of urgency that falls off steeply as the time horizon passes from the domain of the limbic system to the domain of the neocortex, resulting in the characteristic shape of a hyperbolic curve: