Exoskeletons are central to the physiology and survival of marine invertebrates, but future increases in the temperature and pCO2 of the marine environment may alter the biomineralization processes involved in their formation. Thus, it is important to consider the impacts of a changing climate on the functionality of invertebrate exoskeletons. In this study, juvenile blue crab, Callinectes sapidus, from the Chesapeake Bay were exposed to increased temperature and pCO2 in a 2 × 2 factorial design for a period of two molts (approximately 30 days). Treatment levels were chosen to represent current (26 °C and 800 μatm CO2) and predicted future conditions in the year 2100 (32 °C and 8000 μatm CO2) in the Chesapeake Bay. Thickness was determined by light microscopy and carapace calcium (Ca) and magnesium (Mg) content were determined by Inductively Coupled Plasma – Atomic Emission Spectrometry. All Ca and Mg in the carapace were assumed to be present in the form of high‑magnesium calcite (HMC). Increased temperature decreased the thickness of juvenile blue crab carapaces by 8.5% and significantly reduced weight percent HMC by 2.0% (P < 0.05). Increased pCO2 significantly increased weight percent HMC by 2.0% but a significant increase in Mg content was also found. The observed counteractive effects of temperature and pCO2 on weight percent HMC underscore the importance of assessing such interactions in studies that quantify the impacts of multiple environmental stressors. Combined with new data regarding the influence of increased temperature and pCO2 on blue crab growth, the results of this study indicate tradeoffs between carapace thickness and chemistry with growth in juvenile blue crab exposed to future warming.