Which federal agencies formulate and execute policies regarding climate change?

Strictly speaking, this question asks who
formulates and who executes policy, and it restricts the question to federal agencies. But let's
look a little more broadly.

First, Congress defines the broad issues of how
the government enacts policies with regards to climate change. It does so by creating or
modifying agencies and by writing legislation to address specific issues it considers
important. 

Second, many interpretations of that legislation end up in front
of the courts, who increasingly have had a greater hand in deciding issues involving climate
change. 

But among the agencies themselves, we have those who monitor, those
who manage, and those who enforce. Among the monitors we have agencies such as NOAA (National
Oceanic and Atmospheric Administration) and US Geological Survey (USGS); they collect data and
prepare briefs on critical changes in the climate. Other agencies who also monitor include
Centers for Disease Control and Prevention (CDC) and various fisheries and wildlife
agencies. 

Among those who manage are the Department of Agriculture, US
Forestry Service, and Department of Energy, to name a few. They are empowered to define
practices in farming, logging, fuel use, and other areas that can have an effect on climate
change.

When it comes to enforcing, the lead agency -- as the name suggests
-- is the Environmental Protection Agency (EPA). The EPA has statutory powers to enforce actions
that the other agencies mentioned often do not. An EPA notice can close down a business and the
EPA can extend well beyond its legislative mandate to take action on hazards causing climate
change. Where the EPA may not have full power to act, as in the case of commercial long-haul
trucks, other agencies such as the Department of Transportation and Department of Energy may
step in. However for most practical matters involving climate change, the lead enforcer is the
EPA. It counts on many Federal and state agencies to provide it with the data to support its
position and to identify violators. And certain major parts of the environmental economy that
involve large-scale policy such as acceptable crops or logging practices are managed by other
agencies better equipped to deal with the issues.