Among the many themes that investors​ in exchange-traded funds (ETFs) can evaluate this year, two of the more obvious ones are tumbling oil prices and the ongoing resurgence in emerging markets equities. With many developing economies still heavily dependent upon commodities production, including oil, it is perhaps somewhat surprising that emerging markets ETFs are performing well this year, given that oil ranks as one of 2017's worst-performing commodities.

It is often better to be safe than sorry, and getting some of that safety comes with rewards. Consider the overlooked SPDR MSCI Emerging Markets Fossil Fuel Reserves Free ETF (EEMX). As the ETF's name implies, this fund eschews shares of fossil fuels producers. EEMX, which debuted in October, tracks the MSCI Emerging Markets ex Fossil Fuels Index. "The MSCI Emerging Markets ex Fossil Fuels Index is designed to measure the performance of companies in the MSCI Emerging Markets Index that do not own proved and probable coal, oil or natural gas reserves used for energy purposes," according to State Street. (See also: Can OPEC Live With $60 Oil?)

In essence, EEMX is an ex-fossil fuels equivalent of the widely followed MSCI Emerging Markets Index. The exclusion of fossil fuels producers (EEMX has a 0.57 percent weight to the energy sector) is working, as EEMX is outpacing the traditional MSCI Emerging Markets Index by 70 basis points year to date. The MSCI Emerging Markets Index allocates almost 7.2 percent of its weight to the energy sector. With EEMX avoiding that sector, that ETF's geographic and sector allocations differ considerably from the emerging markets benchmark. For example, Brazil and Russia, although they are not members of the Organization of Petroleum Exporting Countries (OPEC), are two of the largest emerging markets oil producers. Those countries combine for nearly 11 percent of the MSCI Emerging Markets Index but just 7 percent of EEMX.

Interestingly, EEMX is overweight Mexico, one of Latin America's largest oil producers, and Indonesia, an OPEC member, relative to the MSCI benchmark. Another significant difference between EEMX and the MSCI Emerging Markets Index is number of holdings – EEMX holds just 322 stocks compared to about 830 in the emerging markets index. (See also: Encouragement for Indonesia ETFs.)

A perk of EEMX is that it reduces exposure to state-run companies by trimming energy, but there are drawbacks, too. While EEMX fits the bill as an option for investors looking to apply environmental consciousness to investing, the risk with this fund is obvious – if oil prices rebound, EEMX could lag more traditional emerging markets strategies with standard exposure to the energy sector. (See also: Go Green With Socially Responsible Investing.)