3) Climate change is a risk management issue, not a binary choice between action and inaction.
In many public policy areas, we make decisions about the future in the face of incomplete or imperfect knowledge. For example, we make decisions about our military resources, even though we don’t know exactly where the next conflict might occur. Or we make decisions about infrastructure with limited knowledge of when, where, or how severe the next earthquake will be.
In the face of these other public policy issues, we use the best information at our disposal about future conditions to inform the decisions we must make today. Climate models (as a group) have projected warmer temperatures than has been experienced over the recent decade or so. But this discrepancy does not invalidate models’ utility in understanding how greenhouse gases can warm the planet, as confirmed by observations and fundamental scientific understanding (see Figure 3).
In the end, models should not be seen as magic black boxes that predict the future, but as illustrative tools for a range of potential futures. And what’s clear is that none of these futures looks like the past.
Aside from models, there are many other ways to identify risks, such as examining changes that have occurred to date and pinpointing critical vulnerabilities. Rising sea levels, increasing frequency and severity of heat waves, more intense precipitation events, and changes in ecosystems are climate change impacts now. Extreme weather events demonstrate the potential vulnerabilities of our communities. There are steps we can take to reduce our emissions and build resilience to help manage these risks, even if models are incomplete or imperfect.
The bottom line: The Earth has warmed during the 20th and early 21st centuries, with greenhouse gas emissions from human activities playing an important role. The ability of computer models to simulate some of the most prominent features of the climate system provides high confidence that the rising concentrations of atmospheric greenhouse gases will continue to warm the planet. In the absence of policies to curtail these emissions, the warming is likely to be substantial, bringing an increased risk of many unwanted impacts.