As mudancas climaticas, especialmente o aumento da temperatura e da concentracao de gases de efeito estufa na atmosfera , afetarao o crescimento e desenvolvimento das plantas. O objetivo deste trabalho foi avaliar o efeito de aumento da temperatura e da concentracao de CO2 na emergencia de plântulas de cebola das cultivares Alfa Sao Francisco, Franciscana IPA 10, Vale Ouro IPA 11 e Serena .O experimento foi conduzido em câmaras de crescimento, com controle de umidade, luminosidade, temperatura e CO2, durante 12 dias. O delineamento experimental utilizado foi o inteiramente casualizado, em esquema fatorial 4x4x2, com quatro cultivares de cebola, quatro temperaturas (25 oC; 28 oC; 31 oC e 34 oC) e duas concentracoes de CO2 (380 e 770 ppm) e , com quatro repeticoes e 36 sementes por tratamento. Sementes de cebola das cultivares Alfa Sao Francisco, Franciscana IPA 10, Vale Ouro IPA 11 e Serena foram semeadas em bandejas de polietileno com 36 celulas contendo substrato comercial e mantido nas diferentes concentracoes de CO2 e temperatura. Foram avaliados a porcentagem de emergencia, tempo medio de emergencia, velocidade de emergencia, indice de velocidade de emergencia, comprimento da parte aerea e comprimento da raiz principal. Os dados foram submetidos a analise de variância e as medias comparadas pelo teste de Scott Knott a 5% de probabilidade. As concentracoes de CO2 e as diferentes temperaturas proporcionaram efeitos significativos entre as cultivares para a maioria das variaveis analisadas. O aumento de CO2 e temperatura influenciaram no processo de emergencia de plântulas de cebola. Normal 0 21 false false false PT-BR JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-fareast-language:EN-US;} Climate change, especially atmosphere temperature and concentration of greenhouse gases increase, will affect plant growth and development . The aim of this study was to evaluate the effect of increased temperature and CO2 concentration in emergence of seedlings of onion cultivars Alfa San Francisco, Franciscan IPA 10, Valley IPA 11 Gold and Serena. The experiment was conducted in growth chambers with humidity, light, temperature and CO 2 control during 12 days. The experimental design was completely randomized in a 4x4x2 factorial scheme, with four onion cultivars , four temperatures (25 °C; 28 °C, 31 °C and 34 °C and two concentrations of CO2 (380 to 770 ppm), with four replications and 36 seeds per treatment. Seeds of onion cultivars Alfa Sao Francisco, Franciscana IPA 10, Vale Ouro IPA 11 and Serena were sown in plastic trays with 36 cells containing commercial substrate and placed in different CO 2 concentrations and temperature. Emergence percentage, average time of emergence, emergence speed, emergence speed index, shoot length and root length was evaluated. The data were submitted to variance analysis and the averages compared by Scott Knott test at 5% probability. The CO 2 concentrations and different temperatures produced different effects among cultivars for most of the variables. The increase of CO 2 and temperature influence the emergence onion seedlings process. Key-words: climate change, impacts, agriculture