As I'm sure many of you have done, I've let my elected representatives know that we need strong action to address climate change. There's no doubt that letters, emails, phone calls, and direct lobbying have been making a difference. For example, the Bi-Partisan House Climate Solutions Caucus is a result, in large part, of the lobbying efforts of Citizen's Climate Lobby.

But there are still far too many elected officials who are looking for more than a small cadre of dedicated citizen activists and volunteer lobbyists to convince them that climate change should be a top priority. They want to hear from more of their constituents and, more importantly, from community leaders. That's why we need to get endorsements from a broad range of constituents including CEOs, religious leaders, thought leaders, and any others with a voice respected by our elected officials.

There are a number of climate-action endorsement letters circulating. For example, Citizen's Climate Lobby is looking for people to endorse the following statement:

WHEREAS... The costs of climate change -- including destabilized weather patterns, rising sea levels, extreme weather events, and other serious impacts -- now pose a substantial threat to the health, prosperity and security of Americans. The costs are real, they are growing, and they are already burdening businesses, taxpayers, municipal budgets and families. Our economy, infrastructure, public safety and health are directly at risk.

Prudent action now will be far less costly than the consequences of delayed response and will create a more stable business environment for our nation.

I certainly agree with that statement and it should become easier and easier to find community leaders who could make such an endorsement. But, at this point, that statement is too weak to convince elected officials to support policies that will be necessary and sufficient to avoid the most catastrophic consequences of climate change. Specifically, it's too weak because it does not commit to keeping average global temperatures to 1.5 degrees above preindustrial levels.

You might be asking: "Why not just try to get broad endorsements now and worry about specific targets later." Because it already is later and because this is not the kind of issue where 'every little bit that we can do helps.' It is the kind of issue that has tipping points and thresholds we should not pass.

The target that has been the focus of international climate conferences is to keep average global temperatures below 2 degrees Celsius. But that target has more to do with political expediency than with any basis in scientific evidence. A growing body of climate change literature suggests that a world at 2 degrees average would be unrecognizable to us and would likely be unsustainable for the growing human population. In short, it's a bad target.

The difference between 2 degrees of warming and 1.5 degrees turns out to be far more substantial than that half a degree might suggest. A recent study found that there would be significantly greater crop yields and availability of fresh water in a 1.5 degree world than in a 2 degree world. It would also give us greater protection against run away global warming that is likely to occur at 2 degrees.

Given that, I propose getting broad endorsement of the following statement:

I endorse efforts by the United States aimed at limiting global average temperature increases to 1.5 degrees C above preindustrial levels. A growing body of climate science studies suggest that warming over 1.5 degrees C would lead to substantial decreases in the availability of fresh water, substantial decreases in crop yields, severe degradation of the oceans and the potential for triggering feedback loops – such as the melting of Greenland's ice sheets - that would lead to catastrophic warming beyond the control of human activity. I understand that these potential outcomes would have the greatest impact on the poorest populations of the world in the near term and would affect the global community as a whole for many generations into the future. Therefore, I see these risks as unacceptable.

I realize that meeting the 1.5 degree C target will likely mean an economic transformation equal to – if not greater than – the mobilization for World War II, but I also understand that the consequences of surpassing the 1.5 degree C target would cost far more than the costs of such a transformation. Furthermore, I understand that the United States, acting alone, cannot meet the 1.5 degree C target, but I believe that the United States must act as a global leader on this critical issue – even acting unilaterally if necessary – thereby providing a model for other countries to follow.