Vol-sellers beware. That’s the message from Natixis Global Asset Management’s Brett Olsen and Nicholas J. Elward, in their latest note, as they warn “it stands to reason that the market will see a reversion to the mean and find the VIX trading in the 20+ range before too long.”

There has been much discussion lately about how stock market volatility is at near historic lows. The Chicago Board Options Exchange Volatility Index (or VIX), a measure of implied or future volatility, is at a level of roughly 10 as of June 30, 2017. If one looks at the history of the VIX, it has typically averaged closer to 20.

Over the last 20 years, there has been only one other period of volatility this low, over the 2004–2006 timeframe. This period was characterized by economic expansion and a strong stock market as the economy moved out of the 2000–2003 tech bubble burst. This period of calm came to an end with extremely high volatility as we entered the Great Recession of 2008.

There are several factors that could cause the VIX to increase in the coming months; personally, we believe it may double. Here are four reasons why:

1) Geopolitical unrest – There continues to be concern among many market analysts around North Korea, Russia and a variety of Middle Eastern nations – including Turkey, Iran, Saudi Arabia, Syria, and Iraq. Depending upon what a small number of political leaders decide to do in their countries, in their regions, and even more widely, we could suffer increased global unrest, which may cause increased global stock market volatility. In addition to the actions taken by political leaders, the threat of terrorism remains unpredictable and could contribute to rising volatility.

2) Instability in the American political landscape – Ever since the election of Donald Trump in November 2016, we have seen strong stock market returns. The Trump administration has promised investor friendly policies, such as tax reform and deregulation. There are also expectations of more infrastructure spending, which could help increase business growth and employment in the United States. However, despite these expectations, there have been many distractions as these legislative goals are being pursued, including the ongoing investigation into the Trump campaign’s connections with Russia and continued disagreements between and among legislators of both parties. Each of these distractions has the potential to create further frustration among both business leaders and voters alike. Moreover, it remains possible that the investigations into the Trump administration could result in material changes in executive branch leadership. Current political dynamics have the potential to translate quickly into increased market turbulence.