delivered the Opinion of the Court.
This original proceeding arises out of the defendant's motion to dismiss the sexual assault on a child charges against him because they are time barred. The defendant contends that the ten-year statute of limitations in effect when he allegedly committed the crimes mandates dismissal of charges brought more than ten years after the last alleged incident. The People counter that the General Assembly's amendment of the statute of limitations for sexual assault on a child, extending it to ten years after the victim reaches the age of eighteen, was intended to apply retroactively and therefore applies to the charges in this case. The trial court agreed with the People, concluding that the extended statute of limitations applied to the defendant, and denied his motion to dismiss. We issued a rule to show cause and now make that rule absolute, holding that because we are unable to discern the legislative intent behind the amendments to the statute of limitations, we must apply the rule of lenity to bar the charges under the ten-year statute of limitations in effect when the crimes were allegedly committed. We also overrule the court of appeals' recent decision in People v. Boston, - P.3d -, No. 07CR2186, 2009 WL 400073 (Colo.App. Feb. 19, 2009).
I. Facts and Procedural History
The defendant, Eugene Summers, was charged with thirty-two counts of sexual assault on a child, sexual assault on a child by one in a position of trust, sexual assault on a child-pattern of abuse, and criminal attempt to commit sexual assault on a child. The acts were allegedly committed during two separate time periods-one period from August 1, 1992, to August 31, 1993, and one period from August 1, 1995, to June 30, 1996. The felony complaint charging Summers with these crimes was filed April 6, 2007. Summers moved to dismiss the charges against him, contending that they were all barred by the statute of limitations. The statute of limitations in effect at the time of the alleged crimes was ten years. However, the General Assembly amended the statute of limitations in 2002, tolling the ten-year statute of limitations for sexual assault on a child until the child victim reaches the age of eighteen. The trial court denied Summers' motion to dismiss, holding that the newly amended statute of limitations applied to Summers' case and that it had not yet run.1
II. - Analysis
We are asked in this case to determine which statute of limitations applies to the sexual assault on a child charges brought against Summers. Because the plain language of the statute is ambiguous and we are unable to determine any clear intent expressed by the legislature, we hold that the rule of lenity applies and the ten-year statute of limitations in effect at the time of the alleged acts bars the charges against Summers.
A. Ambiguity in Plain Language
The amendments to the statute of limitations for sexual assault on a child were introduced as House Bill 02-1396, which was later enacted as § 18-8-411, C.R.S. (2002). In determining how to apply H.B. 02-1396, *254we begin with the plain language of the statute. Frazier v. People, 90 P.3d 807, 810 (Colo.2004). If the language is unambiguous, we look no further and apply the words as written. Slack v. Farmers Insurance Exchange, 5 P.3d 280, 284 (Colo.2000). If, however, there is ambiguity on the face of the statute, our task is to discern the legislative intent behind the law. Frazier, 90 P.3d at 810. In construing statutory language, we read the statute as a whole, with a goal of giving "consistent, harmonious, and sensible effect to all its parts." People v. Dist. Court, 713 P.2d 918, 921 (Colo.1986).
For purposes of determining the statute of limitations that applies to Summers' alleged crimes, two sentences contained in section 18-8-411 are relevant. The first is contained in subsection (2)(b) and reads, "The ten-year statute of limitations shall apply to all felony offenses specified in subsection (1) of this section which are alleged to have occurred on or after July 1, 1992." §+18-8-411(2)(b), C.R.S. (2002). The second appears in section 18-3-411(5) as published in the Colorado Session Laws and reads, "Except as otherwise provided in subsection (2) of this seetion, this act shall take effect upon passage, and shall apply to offenses committed on or after said date." Ch. 288, see. 5, $ 18-8-411, 2002 Colo. Sess. Laws 1127, 11830.
These two sentences are in direct conflict with one another. The first mandates that the new eighteen-plus-ten statute of limitations be retroactively applied to all crimes for which the ten-year statute of limitations had not yet run when the new law was enacted, including the crimes at issue in this case. If that language is applied, the charges against Summers are not time barred, and he can be tried on the charges. However, the second sentence mandates that the new statute of limitations applies only to crimes committed on or after its effective date of June 3, 2002, implying that the previously existing flat ten-year statute of limitations be applied to all crimes committed before that date. If this language is applied, the flat ten-year statute of limitations applies in this case, and the charges against Summers are time barred. Reading the statute as a whole, it is impossible to give meaning to both of these provisions. We must therefore determine which one controls by inquiring into the legislative intent behind the language used.
B. Legislative Intent
Because we are unable to apply the plain language of the statute, we turn to an analysis of the legislature's intent in enacting the statute. When an ambiguity appears on the face of a statute, "we may rely on other factors such as legislative history, the consequences of a given construction and the goal of the statutory scheme to determine a statute's meaning." Frazier, 90 P.3d at 811. In doing so, we are mindful that "[a]) statute should not be construed in a manner which defeats the obvious legislative intent." Tacoranmte v. People, 624 P.2d 1324, 1330 (Colo.1981).
1. Legislative History
The confusion in this case arises out of a poorly drafted statute-the substantive provisions of the statute indicate that the statute is to apply retroactively, but the effective date clause explicitly states that the statute applies to crimes committed on or after the statute's effective date. In order to understand the conflicting provisions of the law, it is important to consider how the statute was amended.
Prior to the 2002 legislative session, the statute of limitations for sexual assault on a child in Colorado was ten years from the date of the last occurrence of the crime. The statute of limitations at the time read:
No person shall be prosecuted, tried, or punished for an unlawful sexual offense other than the misdemeanor offenses specified in sections 18-38-4022 and 18-3-404, unless the indictment, information, complaint, or action for the same is found or instituted within ten years after commission of the offense.... The ten-year statute of limitations shall apply to all offenses specified in subsection (1) of this section [including the offenses with which the defendant is charged in this case] which are *255alleged to have occurred on or after July 1, 1979.
§ 18-3-411(2), C.R.S. (2001).
The General Assembly amended the law in 2002 to toll the ten-year statute of limitations for sexual assault on a child until the child victim reaches the age of eighteen. The substantive amendments indicated that the new statute of limitations was intended to reach back and apply to crimes committed on or after July 1, 1992. The amended statute of limitations provided:
No person shall be prosecuted, tried, or punished for an unlawful sexual offense charged as a felony unless the indictment, information, complaint, or action for the same is found or instituted within ten years after the victim reaches the age of eighteen years. The ten-year statute of limitations shall apply to all felony offenses specified in subsection (1) of this section [including the offenses with which the defendant is charged in this case] which are alleged to have occurred on or after July 1, 1992.
§ 18-3-411(2)(b), CRS. (2002) (emphasis added). When H.B. 02-1396 was initially proposed,2 it contained a no-appropriations clause.3 Section 3 of the original version of the bill read:
The general assembly hereby finds that the amendments to sections 16-5-401 and 18-3-411, Colorado Revised Statutes, enacted in this act will result in the minor fiscal impact of one additional offender being convicted and sentenced to the department of corrections during the five years following the passage of the act. Because of the relative insignificance of this degree of fiscal impact, these amendments constitute an exeeption to the five-year appropriation requirement specified in section 2-2-703, Colorado Revised Statutes.
H.B. 1396, 68rd Gen. Assem., 2d Reg. Sess. (Colo.2002).
This version of the bill resulted from the Colorado Legislative Council Staffs State and Local Fiscal Impact Report, which analyzed the financial impact of the change in the statute of limitations, and predicted an increase of one offender admitted to the Department of Corrections every five years. Finding an increase of one offender every five years to be minimal, the House attempted to exempt the bill from the requirement that the bill's costs be appropriated in the bill itself.
In addition, section 4 of the bill provided for a retroactive effective date: "Section 4. Effective date-applicability. This act shall take effect July 1, 2002, and shall apply to offenses committed on or after July 1, 1992." Id. (emphasis added). This effective date was consistent with section 2 of the bill, which indicated that the new eighteen-plus-ten statute of limitations should apply to crimes committed on or after July 1, 1992.
H.B. 02-1396 was then reviewed by the Joint Budget Committee (JBC) staff, The JBC staff prepared a Fiscal Analysis Report and presented it to the Senate Appropriations Committee. The JBC staff expressed its concern regarding several sentencing bills that had been introduced during the session and contained no-appropriations clauses indicating that the fiscal impact would only be a one-offender increase. The Report noted that if each of these bills were exempted from the five-year appropriation requirement, the Department of Corrections would be severely underfunded. The JBC staff therefore prepared an amendment for H.B. 02-1396 which transferred funds in order to cover the increased costs resulting from the bill. Sections 8 and 4 of the bill were changed to represent the transfer of funds. *256Section 5 became the new effective date clause of the bill, and it read, "Except as otherwise provided in subsection (2) of this section, this act shall take effect upon passage, and shall apply to offenses committed on or after said date." Ch. 288, sec. 5, 18-3-411, 2002 Colo. Sess. Laws 1127, 1180 (emphasis added). Subsection 2 of that section made the act's effectiveness contingent upon another bill's passage and allocation of appropriate funds.
The amended version of H.B. 02-1396, which contained section 2, purporting to apply the new statute of limitations to crimes committed on or after July 1, 1992, and seetion 4, purporting to apply the entire bill to crimes committed on or after its passage date, was passed by the General Assembly and signed into law by the Governor on June 8, 2002.
Our review of the legislative history behind H.B. 02-1396 fails to clarify the legislative intent behind the bill. It is clear that the bill as initially introduced was intended to apply the new eighteen-plus-ten statute of limitations to crimes committed in the past for which the statute of limitations had not yet run. However, the original version of the bill was not enacted. The legislature, for one reason or another, changed the effective date clause to indicate that the new statute of limitations should only apply to crimes committed on or after its effective date. We must not disregard this language when determining the legislature's intent, as the words used in a statute are the best indicator of legislative intent. People v. Dist. Court, 713 P.2d at 921.
Moreover, the addition of an appropriations clause allocating funds from 2002 to 2007 suggests that the statute was intended to apply retroactively. It could be argued that there would be no need to appropriate additional funds to cover the first five years of the amended statute's enforcement unless the legislature intended for the new statute of limitations to reach back and cover crimes already committed.4 This view would carry more weight if not for the fact that at the very point at which the legislature added the appropriations clause, it also amended the effective date clause to make the statute apply prospectively. We are not persuaded, therefore, that the addition of the appropriations clause clearly indicates that the legislature intended for the statute to apply retroactively.
Additionally, the legislative history might also be interpreted to mean that the change in the effective date clause was simply an unintended drafting error creating an undesirable loophole in the statute of limitations. Even if that were the case, hardships created by statutory language are matters for legislative action; this court is not permitted to rewrite the law in order to avoid an unpopular result. See Busby v. Camp, 16 Colo. 38, 39, 26 P. 326, 326 (1891).
In short, the legislative history of H.B. 02-1396 leaves us with no clear indication of whether the General Assembly intended for the eighteen-plus-ten statute of limitations to apply retroactively or prospectively.
2. Presumption of Prospective Application
Because our review of HB. 02-1896's legislative history fails to reveal the legislative intent behind the bill, we turn to other aids of statutory construction. See Tacorante, 624 P.2d at 1330 ("'The general canons of statutory construction may be applied to determine the correct effective date of a statute."). One such aid in Colorado is the presumption that statutes apply prospectively. § 24-202, C.R.S. (2008). The General Assembly may override this presumption by clearly expressing a contrary intent. Riley v. People, 828 P.2d 254, 257 (Colo.1992). While there is no requirement "that express language of retroactive application" be used *257to convey that intent, Ficarra v. Dep't of Regulatory Agencies, Div. of Ins., 849 P.2d 6, 14 (Colo.1993), the first place we look in determining the legislature's intent is the language used in the statute. See Spahmer v. Gullette, 113 P.3d 158, 162 (Colo.2005).
The presumption of prospective application is only strengthened by the insertion of an effective date clause that explicitly mandates prospective application. It is well established in Colorado that when the General Assembly indicates in an effective date clause that a statute shall apply prospectively, courts are bound by that language. See People v. McCoy, 764 P.2d 1171, 1174 (Colo.1988) (applying statute prospectively where effective date clause stated that amendments "shall apply to acts committed on or after" its effective date of July 1, 1985); People v. Macias, 631 P.2d 584, 587 (Colo.1981) (applying statute prospectively where effective date clause read, "This Act shall take effect July 1, 1979, and shall apply to offenses committed on or after said date"); People v. Patnode, 126 P.3d 249, 258 (Colo.App.2005) (applying statute prospectively where effective date clause said the amendment "shall take effect July 1, 1999, and shall apply to offenses committed on or after said date.").
The cases cited above are not directly analogous to this case, as none of the statutes at issue in those cases involved substantive language that conflicted with the prospective effective date clause. Nonetheless, while we cannot "ignore the clear legislative determination that the ... amendments were intended ... to have prospective effect only," as expressed in the effective date clause, Riley, 828 P.2d at 257, we are not free to simply disregard the conflicting language in section 2 of the statute. The language of that seetion appears to indicate an intent to rebut the presumption of prospective application, using explicitly retroactive language. However, the simultaneous use of a prospective effective date clause weakens that rebuttal considerably. As a result of these conflicting provisions, we are unable to use the presumption of prospective application to discern the legislative intent behind the statute.
3. Subsequent Indications of Intent
We have previously recognized the General Assembly's power to make the legislative intent behind a statute clear in a subsequent version of the statute. See Tacorante, 624 P.2d at 1329-30 (recognizing that subsequent bill amended the effective date of part of a prior bill); see also Pinellas County Planning Council v. Smith, 360 So.2d 371, 372 n. 1 (Fla.1978) (cited with approval in Tacorante, 624 P.2d at 1330) (allowing legislature to correct clerical error in effective date clause).
The legislature has exercised this power with a prior version of the very statutory scheme at issue in this case. Before 1982, the statute of limitations for sexual assault on a child was three years. § 165-401, C.R.S. (1981). In 1982, the General Assembly amended the statute to extend the statute of limitations to ten years. § 16-5-401, C.R.S. (1982). As originally amended, the statute did not indicate whether it was to apply prospectively to crimes committed on or after its effective date, or whether it was intended to reach back as far as possible to cover crimes committed in the past for which the previous statute of limitations had not yet run. However, realizing its mistake, the General Assembly amended the statute again to add a section indicating the legislature's intent for the new ten-year statute of limitations to apply retroactively.5 When determining the appropriate statute of limitations to apply to crimes allegedly committed in 1980, this court used that subsequent declaration of legislative intent to hold that the amended ten-year statute of limitations applied. People v. Holland, 708 P.2d 119, 120-21 (Colo.1985) ("We conclude that the specific and explicit indication of legislative intent in section 16-5-401.1, is sufficient to overcome the general presumptions [of prospective application of statutes]. ...").
It has now been seven years since the adoption of the 2002 amendments at issue in *258this case. The legislature has made no attempt to clarify its intent regarding the retroactive or prospective applicability of this statute. In fact, the legislature again amended the law in 2006 to completely eliminate the statute of limitations for sexual assault on a child. See § 16-5-401, CRS. (2006). In doing so, it clearly indicated its intent for that change to apply retroactively. The substantive amendments to the bill indicate that it is to apply "to sex offenses against children committed on or after July 1, 1996, and to sex offenses against children committed before July 1, 1996, for which the applicable statute of limitations in effect pri- or to July 1, 2006, has not yet run on July 1, 2006." Ch. 119, see. 1, § 16-5-401, 2006 Colo. Sess. Laws 410, 411. The effective date clause for the 2006 amendments simply states, "This act shall take effect July 1, 2006," ch. 119, see. 5, § 16-5-401, 2006 Colo. Sess. Laws 410, 414, with no indication of any legislative intent for the amendments to apply only prospectively.
In sum, we have no attempt by the legislature to clarify its intent behind H.B. 02-1396. We are left with the statute as written, which is contradictory on its face; the legislative history of the statute, which does not compel a particular result; and the presumption of prospective application, which the language of the statute simultaneously enforces and rebuts. Confronted with conflicting language and finding no guidance through the use of statutory construction aids, we are unable to definitively determine whether the General Assembly intended the eighteen-plus-ten statute of limitations to apply retroactively or prospectively.
C. Rule of Lenity
Because we are unable to apply the plain language of the statute and we are unable to discern the legislature's intent behind the statutory language, we reluctantly turn to the rule of lenity-a rule of last resort invoked only "if after utilizing the various aids of statutory construction, the General Assembly's intent remains ob-seured." People v. Thoro Prods. Co., 70 P.3d 1188, 1198 (Colo.2003). Under the rule, "ambiguity in the meaning of a criminal statute must be interpreted in favor of the defendant." Id. Due to our conclusion that the amended statute of limitation's coverage is ambiguous, the rule of lenity requires that we apply the flat ten-year statute of limitations in effect when the acts allegedly took place. See Id. at 1199 ("Based on the rule of lenity, we accordingly construe this ambiguity in favor of the [defendants] and hold that their prosecution is barred by the statute of limitations."). We do not resort to the rule of lenity lightly, but we are mindful that a court should "not attributle] to [the legislature], in the enactment of criminal statutes, an intention to punish more severely than the language of its laws clearly imports in the light of pertinent legislative history." Prince v. United States, 352 U.S. 322, 329, 77 S.Ct. 403, 1 L.Ed.2d 370 (1957). Where, as here, both the statutory language and the legislative history leave us with no way to definitively determine the statute's intended coverage, it is not our place to choose between two competing and viable alternatives in order to usurp the General Assembly's role in making the law. See United States v. Santos, - U.S. -, -, 128 S.Ct. 2020, 2025, 170 L.Ed.2d 912 (2008)(plurality opinion)(noting that the rule of lenity "keeps courts away from making criminal law in [the legislature's] stead"). Rather, we have no choice but to apply the rule of lenity in favor of the defendant. As a result, the charges against Summers are time barred and must be dismissed.
III. People v. Boston
The court of appeals recently addressed the issue we resolve here in an opinion announced after certiorari was granted in this case. The court of appeals reached a different conclusion than we reach today, essentially writing the effective date clause out of the statute to find that there was no conflict on the face of the statute and that the eighteen-plus-ten statute of limitations applied retroactively. To the extent that the court of appeals' opinion is inconsistent with ours, it is overruled.
The court provided two lines of reasoning to support its conclusion that the eighteen-plus-ten statute of limitations should apply *259retroactively. First, it reasoned that the effective date clause was inserted into H.B. 02-1396 together with a safety clause for two purposes-showing when the act became effective and protecting the bill from the referendum process-and therefore could be ignored when interpreting the bill. Boston, - P.3d at -, 2009 WL 400073, at *2. Second, it determined that because the effective date clause appears only in the Colorado Session Laws, and not in the Colorado Revised Statutes, it is "not considered to be a part of the official statutes of the state." Id. at --, at *3. We find neither line of reasoning persuasive.
We reject the court of appeals' contention that the General Assembly's alleged intention behind the effective date clause renders the language in that clause meaningless. There is no evidence to show that the only purpose behind the effective date clause was to protect the bill from the referendum process, and the court provided no analysis explaining why it believed that to be the General Assembly's intent. Even if the effective date clause were only inserted to avoid the referendum process, we cannot simply disregard the legislature's indication that the statute was intended to apply prospectively. See Riley, 828 P.2d at 257. The court of appeals' decision to essentially ignore the effective date clause based upon the legislature's alleged intent was error.
The court of appeals' second line of reasoning, that anything not appearing in the Colorado Revised Statutes is not officially part of the laws of this state, is likewise erroneous. The court cited section 2-5-118(1)(a) of the Colorado Revised Statutes and Suncor Energy (USA) v. Aspen Petroleum Prods., Inc., 178 P.3d 1263 (Colo.App.2007), to support its conclusion. - This reliance is misguided. While the Colorado Revised Statutes are considered the official publication of statutes in Colorado, § 2-5-118(1)(a), C.R.S. (2008), the reviser is required to include references to the Colorado Session Laws to permit the reader to locate the original source of legislation published in the Colorado Revised Statutes. See § 25-102(a), C.R.S. (2008); see also People v. Washington, 969 P.2d 788, 789 (Colo.App.1998). We consistently reference Colorado Session Laws when interpreting statutes. See, eg., Kufman v. People, 202 P.3d 542, 548 (Colo.2009); Avalanche Indus., Inc. v. Clark, 198 P.3d 589, 592 (Colo.2008); Gallion v. Colo. Dep't of Revenue, 171 P.3d 217, 221 (Colo.2007). In addition, the Colorado constitution provides that a statute "take[s] effect on the date stated in the act, or, if no date is stated in the act, then on its passage." Colo. Const. art. V, see. 19. We are not free to simply ignore language which is given meaning by our constitution. The court of appeals erred in reasoning that, because the effective date clause appeared only in the Colorado Session Laws, and not in the Colorado Revised Statutes, it need not be enforced.
Because neither line of reasoning provided by the court of appeals in Boston was correct, and because the analysis we conduct today compels a different result, that case is overruled.
IV. Conclusion
We conclude based on the rule of lenity that the eighteen-plus-ten statute of limitations applies to crimes committed on or after the statute's effective date, as stated in the effective date clause. As a result, the charges against Summers are time barred by the flat ten-year statute of limitations in effect at the time of the alleged acts. We therefore make the rule to show cause absolute and remand for proceedings consist with this opinion.
Justice COATS concurs in the judgment. Justice EID dissents.. The victim in this case was born December 19, 1981, and turned eighteen December 19, 1999. If the 2002 amendments apply in this case, the statute of limitations does not bar charges until December 19, 2009.
. It is appropriate for us to consider successive drafts of legislation in discerning the legislative intent behind a statute. See Singer & Singer, Sutherland Statutory Construction 558-59 (Ith ed.2007).
. Colorado law requires that all bills "which would result in a net increase in periods of imprisonment in state correctional facilities" contain "an appropriation of moneys which is sufficient to cover any increased capital construction costs and any increased operating costs which are the result of such bill in each of the first five years in which there is a fiscal impact as a result of the bill." § 22-703, C.R.S. (2008). In order to attempt to exempt a bill from this requirement, the General Assembly must make such intent explicit in the text of the bill with a no-appropriations clause. See id.
. If the statute applied prospectively only, there would be no fiscal impact within the first five years after its enactment. Any crimes committed on or after the statute's effective date would necessarily already be covered by the flat ten-year staiute of limitations already in effect. There would therefore be no fiscal impact until ten years after the statute went into effect, when charges previously barred could be brought pursuant to the new eighteen-plus-ten statute of limitations. Nonetheless, the appropriations clause appropriates funds for the years 2002 through 2007, the first five years in which the statute was effective.
. The following section was added to the statute: ''The intent of the general assembly in enacting section 16-5-401(6) and (7) in 1982 was to create a ten-year statute of limitations as to offenses specified in said subsections committed on or after July 1, 1979." § 16-5-401.1, C.R.S. (1985).