The sun, the breeze, the return of ice cream stands [1] ... April is the worst month to be cooped up in the office. But instead of zoning out on gossip blogs and staring-out-the-window dreaming, put your spring-fever indolence to good use. Here are some valuable - and slightly alarming - online tools to calculate environmental impact statements for yourself, your office, your family.

- With our hyperactive driving habits and energy-voracious homes, Americans produce more CO2 per capita than any other industrialized nation. Use the carbon calculator [2] from Climate Crisis or the personal pollution inventory [3] from Environmental Defense [4] to estimate your contribution.

- According to sustainability [4] advocates Redefining Progress [5], the human population's ecological footprint - how much land and water we currently use to support ourselves - exceeds the earth's capacity by almost 40 percent. Their ecological footprint quiz [6] measures yours in terms of how many identical Earths it would take to sustain a world population if everyone lived like you.

- Native Energy's carbon footprint calculator [7] lets you track the amount of carbon you produce as well as what you've done to offset it - like paying for shares of wind turbine construction through their WindBuilders [8] project.