Temperature increases are predicted as part of global climate change which applies not only to air, but also to soil temperatures. To study the effects of rising temperatures at ecosystem scales, numerous long-term warming experiments have been established worldwide during the past decades that not only warm the vegetation, but also whole soil profiles. Their aim is to better predict ecosystem responses to warming also with respect to carbon cycling within the soils. We investigated soil and plant samples of several long-term warming experiments located in temperate and boreal ecosystems in the United States of America for cycling of bulk carbon as well as plant- and microorganism-derived organic matter. We were rather surprised, how fast carbon cycling changed and that specifically subsoil carbon became very vulnerable to decomposition with warming. Respective results will be shown and put in a bigger perspective in terms of better understanding of ecosystem responses in a warmer future.