California's forests have always been an important part of our heritage and our daily lives. We rely on them for water, wood and recreation. We are likely to rely on them even more as a powerful resource to help combat climate change.

Recent polls indicate that almost 90 percent of Californians support protecting forests because they naturally remove global warming pollution from the atmosphere. The good news is that the state's Air Resources Board, charged with implementing California's landmark global warming policy, wisely included forests among the sectors that must help the state meet its targets for reducing carbon dioxide, the primary global warming pollutant.

The board's challenge is to ensure that the true climate benefits of forests are accounted for accurately, realistically and over time. Getting these numbers right is the key to success. Failure to do so will have serious consequences for our forests – and the climate benefits that we need from them.

Forests have a natural role in regulating our climate and can be managed like a growing, long-term "carbon bank." They use photosynthesis to absorb carbon dioxide from the atmosphere and sequester, or hold, it as carbon for very long periods of time. The older forests are, the more carbon they hold. That is why California's legendary redwood and Sierra forests are some of the best carbon banks in the world.

Keeping track of forest carbon requires double-entry bookkeeping: Trees absorb carbon through photosynthesis when they grow. But when trees are cut down faster than they grow back and forests are cleared for development, most of that stored carbon is released back into the atmosphere, and our bank is depleted.

In other words, depleting our forests actually contributes dramatically to climate change. In fact, forest loss and depletion is the second largest source of global carbon emissions.

The board's current plan rightly recognizes the value of our forests as carbon banks by proposing a target of "no net loss" of forest carbon while seeking to increase net savings in our carbon banks. The plan also recognizes that forests have a role in meeting climate goals in other sectors, like land-use, construction and energy.

The fact that many sectors rely on forests presents an accounting challenge. For example, right now the plan only addresses the climate benefits of burning wood as a low-carbon biomass fuel in the energy sector without taking into account the climate cost of harvesting that wood in the forest sector.

It's like having a family checkbook, where different family members can write checks from the same account – in this case, the same carbon storage bank. Someone needs to know what everyone is drawing from the account in order to maintain a healthy balance and ensure that we don't exceed the limit.

When it meets Nov. 20 to finalize the plan for implementing Assembly Bill 32, the Air Resources Board should add provisions for much tighter accounting for all forest-related climate costs and benefits. They must require that any impacts on forests' carbon banks are accurately tracked across different sectors, like the family checkbook, so we can track unwanted withdrawals. This will give us "accounting with accountability" and the ability to clearly identify the causes of unexpected gains or losses and to respond accordingly with forest management that maximizes climate benefits and minimizes losses.

The plan also needs to take a long-term view. Forests increase their carbon stores as they get older, much like compound interest in a bank account. Clearing our forests to generate more products, like woody biomass, might look like a big win for climate in the first few years. But when we factor in the long-term, compounded impact of lost carbon storage, it's likely a climate disaster.

Conserving and restoring our forests using sustainable management that increases carbon stores over time should be central to California's efforts at healing the climate. But using fuzzy math to calculate the climate impact of forests won't just cook the books – it will cook our planet.

Laurie Wayburn is president and co-founder of the Pacific Forest Trust and a 2008 recipient of The James Irvine Foundation Leadership Award for pioneering market-based solutions to protect forests as a way to address climate change.