NEW YORK (TheStreet) -- The concept of global warming is as important as it is politically controversial. The planet simply getting warmer turned out to be too simple as the planet got a little cooler for a couple of years, so the term "climate change" came to be.Unless anyone has refuted the last ice age, occurring approximately 22,000 years ago, we know that climate does change on some sort of cycle, even if it is not yet fully understood by modern science. So the question really becomes whether or not mankind could be accelerating the movement of the pendulum toward a warmer planet. An anecdote to support the idea that man is precipitating a warmer planet can be found in Arizona where I live. My wife grew up in Phoenix, and from the time she was born in the early 1970s to now the population has almost tripled. Since I moved to Arizona in 1990 it has increased by 50%. The growth is accelerated by paving over what used to be agricultural land or empty desert into urban and suburban neighborhoods. The new pavement is holding in the summer heat. Studies show the summer highs in Arizona are not really increasing but the overnight lows during the summer have been rising, and in the winter there have been fewer frost days during the winter. This type of trend will, I hope, lead to changes in how we do things. There are several ways to participate in how this will evolve through exchange traded funds including wind, solar and clean tech ETFs. Our firm's preferred way of accessing the theme is through the PowerShares Water Portfolio ( PHO). According to the World Resources Institute, global water consumption grew at twice the rate of the population during the 20th century. Hydrogen Ventures estimates that $660 billion will be needed for water infrastructure in the next 20 years. If the planet is getting hotter, then it follows logically that it is getting drier. In addition to climatological reasons for increased demand for water, in places like China pollution serves as another catalyst for water demand.
In addition to PHO, investors can also consider the PowerShares Global Water Portfolio ( PIO) and the Guggenheim S&P Global Water Index ETF ( CGW). The three funds are very similar although PHO differs slightly because it allocates 64% to the industrial sector compared to 46% in PIO and 47% in CGW. The second-largest sector in all three funds is utilities, which make up 17% of PHO, 45% of PIO and 38% of CGW. The heavy weightings to these two sectors capture hardware like water testing and filtration and the companies that, like an electric company, distribute water to homes and businesses. PHO's tilt to industrials give it a lower yield than the other two funds at less than 1%, but none of the three offer much yield -- PIO and CGW yield less than 2%. As the name of the funds indicate, PIO and CGW are global funds and PHO is focused on domestic stocks, although PHO actually has one Brazilian ADR and one French ADR. The U.S. is the largest country in on both PIO and CGW followed by the UK. All three funds have been trading for several years, PHO is the oldest, having started trading in 2005. Not surprisingly, they all correlate very closely. Each fund has had times leading the group and lagging the group, which makes picking one as the best choice impossible. Going forward they will all capture the theme and continue to closely correlate with each other. At the time of publication the author had no position in any of the stocks mentioned. Follow @randomroger This article was written by an independent contributor, separate from TheStreet's regular news coverage.