Purpose: This study explores the inherent instability, if any, in the context of investment in stocks of environment friendly companies (or the “green” stocks) across the globe using the time-series momentum trading strategies. Design/Methodology/Approach: Using the monthly data for the Green Indexes from the US, the Europe and the Asia-Pacific region over 2003-2019, the authors construct time series momentum trading strategies to examine the efficacy of regional green indexes as well as two diversified global green portfolios to offer abnormal return to attract investors, particularly speculators. We explore further whether such strategies could operate as hedging instrument. A comparison of results across different regions helps us establish a universal nature, if any, of investment in green stocks. Findings: The study finds that regional green indexes are unable to outperform the market. The global green portfolios perform significantly better. The inefficacy of the relevant time-series momentum trading strategies rules out the possibility of speculations. However, number of profitable momentum strategies are significantly higher for the diversified portfolios in longer run. The portfolios perform significantly better in outperforming the buy-only strategies as well. The stable market, escalated demand, and the resulting increment in valuation of green stocks make adoption of greener technologies a choice rather than a forced obligation. This offer a solution to the problem of Tragedy of Common. Originality/value: Sustained increase in investment in green stock is one of the most important forms environment perspective since better valuation of their stocks would indubitably convince firms to reduce their carbon footprints. A continued enthusiasm however would require investors’ faith in it. Presence of momentum profit would invite speculators leading to irrational exuberance, dwindling confidence and consequent fragility. Literature on green investment is relatively sparse with the threat of its vulnerability issues left largely unnoticed. Our study fills these gaps.