When dealing with an issue like greenhouse gas-induced climate change, productive discussion needs to stay focused on the practical questions: what is the general nature of the risk, and how can we mitigate the risk. Discussions of climate change often become sidetracked by non-productive investigations into the detailed nature of the risk, which are often initiated by individuals who are afraid that general recognition of risk implies that particular strategies/policies must be adopted. I hope to keep this discussion on track by starting with these two declarations:

Before getting into the details, let's consider the nature of risk and uncertainty with respect to climate change. We don't know what our climate will be like in the future. It might be similar to today's, or it might be worse. We often wish to refrain from developing plans/opinions until we have a clear sense of what to expect in the future, but this prudence becomes paralytic in situations where we will never have high confidence in our predictions. Some degree of uncertainty is unavoidable with any prediction, and this is especially true with climate predictions due to the complexity of the system. Just to become an expert on this topic would require about 10 years of full time study, and even the experts don't know what will happen. Obviously, most of us cannot become experts, yet we still need to decide how we will act. So, let us begin:

Greenhouse gas emissions (GGEs) create a substantial risk of problematic climate change.

1. Carbon dioxide is a greenhouse gas: it allows visible light to pass, but prevents the passage of infra-red light. The net effect is that energy from the sun can easily reach the surface of the earth, but it is hindered from leaving the earth. 

2. Humans are drastically increasing the amount of carbon dioxide in the atmosphere (about 25% since 1900). 

By themselves, these facts give us reason to consider how to reduce GGEs. But we still may wonder if these changes in atmospheric carbon dioxide levels can impact atmospheric temperatures. So we look at fact 3:

3. Atmospheric temperature is strongly correlated with carbon dioxide concentrations. This has been seen over the long term (ice cores) and over the short term (modern monitoring).

3b. We also know that the size of glaciers is inversely correlated with atmospheric carbon dioxide, both over the long term and the short term.

This doesn't prove that carbon dioxide levels cause an increase in atmospheric temperature or glacier-melt, but the data is consistent with that proposal. Warming may have all types of side-effects, while excessive glacier-melt will impact the entire water system of the earth, ranging from glacier-fed rivers to the ocean itself. As a practical matter, we face a substantial risk that carbon dioxide emissions will cause global warming and climate change. If these facts aren't enough to convince you that we face a risk of GGE-induced climate change, here's one last fact:

4. The experts agree that we face a risk of GGE-induced climate change. 

The Earth is warming. Glaciers are melting. It's time to admit that there is a risk of GGE-induced climate change, and figure out what we want to do about it:

We have many options for dealing with the risk of GGE-induced climate change.