The sun, the breeze, the return of ice cream stands ... 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 from Climate Crisis or the personal pollution inventory from Environmental Defense to estimate your contribution.

- According to sustainability advocates Redefining Progress, 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 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 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 project.